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	$52.36	9.345%	$57.253	$57.25	$57.25	$57.30
Purchase #2	$243.72	7.669%	$262.4109	$262.41	$262.40	$262.40
Purchase #3	$169.52	4.126%	$176.5144	$176.51	$176.50	$176.50
Purchase #4	$191.70	4.375%	$200.0869	$200.09	$200.10	$200.10
Purchase #5	$26.83	9.361%	$29.3416	$29.34	$29.35	$29.30
Purchase #6	$119.62	12.298%	$134.3309	$134.33	$134.35	$134.30
Purchase #7	$106.43	4.401%	$111.114	$111.11	$111.10	$111.10
7 purchase totals =	$910.18		$971.0517	$971.04	$971.05	$971.00