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	$7.40	10.180%	$8.1533	$8.15	$8.15	$8.20
Purchase #2	$137.35	7.733%	$147.9713	$147.97	$147.95	$148.00
Purchase #3	$89.90	11.438%	$100.1828	$100.18	$100.20	$100.20
Purchase #4	$126.65	11.446%	$141.1464	$141.15	$141.15	$141.10
Purchase #5	$75.34	4.199%	$78.5035	$78.50	$78.50	$78.50
Purchase #6	$68.70	4.430%	$71.7434	$71.74	$71.75	$71.70
Purchase #7	$103.87	7.784%	$111.9552	$111.96	$111.95	$112.00
7 purchase totals =	$609.21		$659.6559	$659.65	$659.65	$659.70