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	$170.70	11.512%	$190.351	$190.35	$190.35	$190.40
Purchase #2	$173.30	6.502%	$184.568	$184.57	$184.55	$184.60
Purchase #3	$223.89	4.785%	$234.6031	$234.60	$234.60	$234.60
Purchase #4	$68.89	9.685%	$75.562	$75.56	$75.55	$75.60
Purchase #5	$235.73	10.372%	$260.1799	$260.18	$260.20	$260.20
Purchase #6	$41.54	11.332%	$46.2473	$46.25	$46.25	$46.20
Purchase #7	$87.37	3.590%	$90.5066	$90.51	$90.50	$90.50
7 purchase totals =	$1,001.42		$1,082.0179	$1,082.02	$1,082.00	$1,082.10