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	$133.95	3.244%	$138.2953	$138.30	$138.30	$138.30
Purchase #2	$200.55	12.477%	$225.5726	$225.57	$225.55	$225.60
Purchase #3	$119.25	9.341%	$130.3891	$130.39	$130.40	$130.40
Purchase #4	$158.46	7.605%	$170.5109	$170.51	$170.50	$170.50
Purchase #5	$47.74	11.841%	$53.3929	$53.39	$53.40	$53.40
Purchase #6	$242.90	4.609%	$254.0953	$254.10	$254.10	$254.10
Purchase #7	$52.69	9.873%	$57.8921	$57.89	$57.90	$57.90
7 purchase totals =	$955.54		$1,030.1482	$1,030.15	$1,030.15	$1,030.20