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	$45.67	9.712%	$50.1055	$50.11	$50.10	$50.10
Purchase #2	$41.72	3.810%	$43.3095	$43.31	$43.30	$43.30
Purchase #3	$36.69	9.840%	$40.3003	$40.30	$40.30	$40.30
Purchase #4	$221.79	13.243%	$251.1616	$251.16	$251.15	$251.20
Purchase #5	$164.25	12.506%	$184.7911	$184.79	$184.80	$184.80
Purchase #6	$184.62	13.127%	$208.8551	$208.86	$208.85	$208.90
Purchase #7	$103.66	4.340%	$108.1588	$108.16	$108.15	$108.20
7 purchase totals =	$798.40		$886.6819	$886.69	$886.65	$886.80