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	$206.46	12.184%	$231.6151	$231.62	$231.60	$231.60
Purchase #2	$117.83	4.672%	$123.335	$123.34	$123.35	$123.30
Purchase #3	$99.56	5.161%	$104.6983	$104.70	$104.70	$104.70
Purchase #4	$153.29	8.428%	$166.2093	$166.21	$166.20	$166.20
Purchase #5	$234.51	9.461%	$256.697	$256.70	$256.70	$256.70
Purchase #6	$196.39	13.706%	$223.3072	$223.31	$223.30	$223.30
Purchase #7	$20.28	12.816%	$22.8791	$22.88	$22.90	$22.90
7 purchase totals =	$1,028.32		$1,128.7410	$1,128.76	$1,128.75	$1,128.70