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	$85.71	7.145%	$91.834	$91.83	$91.85	$91.80
Purchase #2	$35.30	13.473%	$40.056	$40.06	$40.05	$40.10
Purchase #3	$229.47	13.802%	$261.1414	$261.14	$261.15	$261.10
Purchase #4	$111.73	11.733%	$124.8393	$124.84	$124.85	$124.80
Purchase #5	$224.80	8.683%	$244.3194	$244.32	$244.30	$244.30
Purchase #6	$40.35	6.120%	$42.8194	$42.82	$42.80	$42.80
Purchase #7	$13.70	9.430%	$14.9919	$14.99	$15.00	$15.00
7 purchase totals =	$741.06		$820.0014	$820.00	$820.00	$819.90