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	$50.29	11.697%	$56.1724	$56.17	$56.15	$56.20
Purchase #2	$50.98	6.202%	$54.1418	$54.14	$54.15	$54.10
Purchase #3	$234.48	6.664%	$250.1057	$250.11	$250.10	$250.10
Purchase #4	$103.67	7.760%	$111.7148	$111.71	$111.70	$111.70
Purchase #5	$100.73	5.142%	$105.9095	$105.91	$105.90	$105.90
Purchase #6	$246.35	11.179%	$273.8895	$273.89	$273.90	$273.90
Purchase #7	$113.30	3.636%	$117.4196	$117.42	$117.40	$117.40
7 purchase totals =	$899.80		$969.3533	$969.35	$969.30	$969.30