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	$100.61	10.521%	$111.1952	$111.20	$111.20	$111.20
Purchase #2	$48.73	3.274%	$50.3254	$50.33	$50.35	$50.30
Purchase #3	$7.33	11.389%	$8.1648	$8.16	$8.15	$8.20
Purchase #4	$208.66	5.543%	$220.226	$220.23	$220.25	$220.20
Purchase #5	$181.63	4.819%	$190.3827	$190.38	$190.40	$190.40
Purchase #6	$36.62	9.561%	$40.1212	$40.12	$40.10	$40.10
Purchase #7	$155.76	12.673%	$175.4995	$175.50	$175.50	$175.50
7 purchase totals =	$739.34		$795.9148	$795.92	$795.95	$795.90