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	$246.83	12.555%	$277.8195	$277.82	$277.80	$277.80
Purchase #2	$69.42	4.497%	$72.5418	$72.54	$72.55	$72.50
Purchase #3	$57.50	8.717%	$62.5123	$62.51	$62.50	$62.50
Purchase #4	$83.52	11.526%	$93.1465	$93.15	$93.15	$93.10
Purchase #5	$33.41	7.505%	$35.9174	$35.92	$35.90	$35.90
Purchase #6	$236.91	8.258%	$256.474	$256.47	$256.45	$256.50
Purchase #7	$181.58	3.243%	$187.4686	$187.47	$187.45	$187.50
7 purchase totals =	$909.17		$985.8801	$985.88	$985.80	$985.80