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	$139.96	8.705%	$152.1435	$152.14	$152.15	$152.10
Purchase #2	$28.28	10.501%	$31.2497	$31.25	$31.25	$31.20
Purchase #3	$140.42	3.184%	$144.891	$144.89	$144.90	$144.90
Purchase #4	$209.31	12.389%	$235.2414	$235.24	$235.25	$235.20
Purchase #5	$218.47	13.446%	$247.8455	$247.85	$247.85	$247.80
Purchase #6	$67.85	5.575%	$71.6326	$71.63	$71.65	$71.60
Purchase #7	$216.49	11.394%	$241.1569	$241.16	$241.15	$241.20
7 purchase totals =	$1,020.78		$1,124.1606	$1,124.16	$1,124.20	$1,124.00