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	$125.79	9.250%	$137.4256	$137.43	$137.45	$137.40
Purchase #2	$38.83	6.106%	$41.201	$41.20	$41.20	$41.20
Purchase #3	$250.41	12.334%	$281.2956	$281.30	$281.30	$281.30
Purchase #4	$16.72	12.557%	$18.8195	$18.82	$18.80	$18.80
Purchase #5	$33.85	3.191%	$34.9302	$34.93	$34.95	$34.90
Purchase #6	$211.58	4.741%	$221.611	$221.61	$221.60	$221.60
Purchase #7	$40.27	11.479%	$44.8926	$44.89	$44.90	$44.90
7 purchase totals =	$717.45		$780.1755	$780.18	$780.20	$780.10