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	$48.71	11.131%	$54.1319	$54.13	$54.15	$54.10
Purchase #2	$46.87	8.629%	$50.9144	$50.91	$50.90	$50.90
Purchase #3	$73.31	8.618%	$79.6279	$79.63	$79.65	$79.60
Purchase #4	$78.33	11.641%	$87.4484	$87.45	$87.45	$87.40
Purchase #5	$199.57	9.350%	$218.2298	$218.23	$218.25	$218.20
Purchase #6	$154.58	6.558%	$164.7174	$164.72	$164.70	$164.70
Purchase #7	$7.27	4.362%	$7.5871	$7.59	$7.60	$7.60
7 purchase totals =	$608.64		$662.6569	$662.66	$662.70	$662.50