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	$144.62	7.371%	$155.2799	$155.28	$155.30	$155.30
Purchase #2	$226.29	12.750%	$255.142	$255.14	$255.15	$255.10
Purchase #3	$59.28	13.590%	$67.3362	$67.34	$67.35	$67.30
Purchase #4	$242.33	13.873%	$275.9484	$275.95	$275.95	$275.90
Purchase #5	$60.90	7.391%	$65.4011	$65.40	$65.40	$65.40
Purchase #6	$249.89	11.546%	$278.7423	$278.74	$278.75	$278.70
Purchase #7	$207.42	4.263%	$216.2623	$216.26	$216.25	$216.30
7 purchase totals =	$1,190.73		$1,314.1122	$1,314.11	$1,314.15	$1,314.00