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	$231.90	8.417%	$251.419	$251.42	$251.40	$251.40
Purchase #2	$115.56	9.160%	$126.1453	$126.15	$126.15	$126.10
Purchase #3	$42.85	12.277%	$48.1107	$48.11	$48.10	$48.10
Purchase #4	$69.47	3.536%	$71.9265	$71.93	$71.95	$71.90
Purchase #5	$197.83	6.580%	$210.8472	$210.85	$210.85	$210.80
Purchase #6	$74.88	5.411%	$78.9318	$78.93	$78.95	$78.90
Purchase #7	$130.34	9.812%	$143.129	$143.13	$143.15	$143.10
7 purchase totals =	$862.83		$930.5095	$930.52	$930.55	$930.30