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	$74.45	11.682%	$83.1472	$83.15	$83.15	$83.10
Purchase #2	$155.74	8.770%	$169.3984	$169.40	$169.40	$169.40
Purchase #3	$40.28	7.451%	$43.2813	$43.28	$43.30	$43.30
Purchase #4	$54.90	12.495%	$61.7598	$61.76	$61.75	$61.80
Purchase #5	$38.53	4.114%	$40.1151	$40.12	$40.10	$40.10
Purchase #6	$190.72	13.539%	$216.5416	$216.54	$216.55	$216.50
Purchase #7	$128.39	8.626%	$139.4649	$139.46	$139.45	$139.50
7 purchase totals =	$683.01		$753.7083	$753.71	$753.70	$753.70