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	$28.66	12.666%	$32.2901	$32.29	$32.30	$32.30
Purchase #2	$218.65	7.777%	$235.6544	$235.65	$235.65	$235.70
Purchase #3	$192.29	12.830%	$216.9608	$216.96	$216.95	$217.00
Purchase #4	$128.34	11.471%	$143.0619	$143.06	$143.05	$143.10
Purchase #5	$49.35	12.530%	$55.5336	$55.53	$55.55	$55.50
Purchase #6	$141.51	3.537%	$146.5152	$146.52	$146.50	$146.50
Purchase #7	$171.89	7.694%	$185.1152	$185.12	$185.10	$185.10
7 purchase totals =	$930.69		$1,015.1312	$1,015.13	$1,015.10	$1,015.20