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	$186.59	6.179%	$198.1194	$198.12	$198.10	$198.10
Purchase #2	$140.27	8.682%	$152.4482	$152.45	$152.45	$152.40
Purchase #3	$157.85	7.245%	$169.2862	$169.29	$169.30	$169.30
Purchase #4	$102.93	5.616%	$108.7105	$108.71	$108.70	$108.70
Purchase #5	$176.50	7.733%	$190.1487	$190.15	$190.15	$190.10
Purchase #6	$90.57	9.485%	$99.1606	$99.16	$99.15	$99.20
Purchase #7	$150.78	13.303%	$170.8383	$170.84	$170.85	$170.80
7 purchase totals =	$1,005.49		$1,088.7119	$1,088.72	$1,088.70	$1,088.60