Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$151.82	12.643%	$171.0146	$171.01	$171.00	$171.00
Purchase #2	$200.99	11.799%	$224.7048	$224.70	$224.70	$224.70
Purchase #3	$185.66	5.789%	$196.4079	$196.41	$196.40	$196.40
Purchase #4	$242.44	12.742%	$273.3317	$273.33	$273.35	$273.30
Purchase #5	$212.45	13.162%	$240.4127	$240.41	$240.40	$240.40
Purchase #6	$37.61	7.215%	$40.3236	$40.32	$40.30	$40.30
Purchase #7	$155.76	11.579%	$173.7955	$173.80	$173.80	$173.80
7 purchase totals =	$1,186.73		$1,319.9908	$1,319.98	$1,319.95	$1,319.90