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	$86.31	3.247%	$89.1125	$89.11	$89.10	$89.10
Purchase #2	$93.65	13.113%	$105.9303	$105.93	$105.95	$105.90
Purchase #3	$129.38	3.453%	$133.8475	$133.85	$133.85	$133.80
Purchase #4	$140.35	4.191%	$146.2321	$146.23	$146.25	$146.20
Purchase #5	$165.73	5.510%	$174.8617	$174.86	$174.85	$174.90
Purchase #6	$147.39	12.521%	$165.8447	$165.84	$165.85	$165.80
Purchase #7	$36.31	11.541%	$40.5005	$40.50	$40.50	$40.50
7 purchase totals =	$799.12		$856.3293	$856.32	$856.35	$856.20