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	$18.57	7.193%	$19.9057	$19.91	$19.90	$19.90
Purchase #2	$85.26	8.315%	$92.3494	$92.35	$92.35	$92.30
Purchase #3	$172.59	4.818%	$180.9054	$180.91	$180.90	$180.90
Purchase #4	$195.37	13.819%	$222.3682	$222.37	$222.35	$222.40
Purchase #5	$62.85	13.512%	$71.3423	$71.34	$71.35	$71.30
Purchase #6	$179.32	10.261%	$197.72	$197.72	$197.70	$197.70
Purchase #7	$114.85	7.230%	$123.1537	$123.15	$123.15	$123.20
7 purchase totals =	$828.81		$907.7447	$907.75	$907.70	$907.70