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	$50.98	11.685%	$56.937	$56.94	$56.95	$56.90
Purchase #2	$5.32	3.146%	$5.4874	$5.49	$5.50	$5.50
Purchase #3	$102.75	10.483%	$113.5213	$113.52	$113.50	$113.50
Purchase #4	$20.31	13.437%	$23.0391	$23.04	$23.05	$23.00
Purchase #5	$199.67	10.125%	$219.8866	$219.89	$219.90	$219.90
Purchase #6	$20.61	3.526%	$21.3367	$21.34	$21.35	$21.30
Purchase #7	$141.28	6.403%	$150.3262	$150.33	$150.35	$150.30
7 purchase totals =	$540.92		$590.5343	$590.55	$590.60	$590.40