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	$110.77	12.731%	$124.8721	$124.87	$124.85	$124.90
Purchase #2	$234.47	9.153%	$255.931	$255.93	$255.95	$255.90
Purchase #3	$207.52	10.258%	$228.8074	$228.81	$228.80	$228.80
Purchase #4	$80.51	11.332%	$89.6334	$89.63	$89.65	$89.60
Purchase #5	$123.54	13.205%	$139.8535	$139.85	$139.85	$139.90
Purchase #6	$228.82	13.754%	$260.2919	$260.29	$260.30	$260.30
Purchase #7	$178.50	3.176%	$184.1692	$184.17	$184.15	$184.20
7 purchase totals =	$1,164.13		$1,283.5585	$1,283.55	$1,283.55	$1,283.60