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	$53.65	8.798%	$58.3701	$58.37	$58.35	$58.40
Purchase #2	$38.66	12.280%	$43.4074	$43.41	$43.40	$43.40
Purchase #3	$52.76	12.735%	$59.479	$59.48	$59.50	$59.50
Purchase #4	$197.56	9.743%	$216.8083	$216.81	$216.80	$216.80
Purchase #5	$116.73	11.501%	$130.1551	$130.16	$130.15	$130.20
Purchase #6	$63.98	10.513%	$70.7062	$70.71	$70.70	$70.70
Purchase #7	$50.89	3.241%	$52.5393	$52.54	$52.55	$52.50
7 purchase totals =	$574.23		$631.4654	$631.48	$631.45	$631.50