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	$38.58	11.832%	$43.1448	$43.14	$43.15	$43.10
Purchase #2	$58.98	11.520%	$65.7745	$65.77	$65.75	$65.80
Purchase #3	$46.34	9.455%	$50.7214	$50.72	$50.70	$50.70
Purchase #4	$52.33	6.479%	$55.7205	$55.72	$55.70	$55.70
Purchase #5	$122.95	11.812%	$137.4729	$137.47	$137.45	$137.50
Purchase #6	$62.96	13.507%	$71.464	$71.46	$71.45	$71.50
Purchase #7	$230.72	7.566%	$248.1763	$248.18	$248.20	$248.20
7 purchase totals =	$612.86		$672.4744	$672.46	$672.40	$672.50