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	$118.96	13.574%	$135.1076	$135.11	$135.10	$135.10
Purchase #2	$128.86	6.201%	$136.8506	$136.85	$136.85	$136.90
Purchase #3	$95.43	5.148%	$100.3427	$100.34	$100.35	$100.30
Purchase #4	$106.66	12.528%	$120.0224	$120.02	$120.00	$120.00
Purchase #5	$74.71	4.619%	$78.1609	$78.16	$78.15	$78.20
Purchase #6	$184.32	9.684%	$202.1695	$202.17	$202.15	$202.20
Purchase #7	$185.72	5.685%	$196.2782	$196.28	$196.30	$196.30
7 purchase totals =	$894.66		$968.9319	$968.93	$968.90	$969.00