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	$229.88	3.575%	$238.0982	$238.10	$238.10	$238.10
Purchase #2	$99.73	9.849%	$109.5524	$109.55	$109.55	$109.60
Purchase #3	$199.88	13.742%	$227.3475	$227.35	$227.35	$227.30
Purchase #4	$231.55	11.533%	$258.2547	$258.25	$258.25	$258.30
Purchase #5	$198.73	5.480%	$209.6204	$209.62	$209.60	$209.60
Purchase #6	$27.74	12.817%	$31.2954	$31.30	$31.30	$31.30
Purchase #7	$71.50	10.392%	$78.9303	$78.93	$78.95	$78.90
7 purchase totals =	$1,059.01		$1,153.0989	$1,153.10	$1,153.10	$1,153.10