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	$213.69	3.503%	$221.1756	$221.18	$221.20	$221.20
Purchase #2	$82.62	9.137%	$90.169	$90.17	$90.15	$90.20
Purchase #3	$195.59	4.500%	$204.3916	$204.39	$204.40	$204.40
Purchase #4	$145.93	9.537%	$159.8473	$159.85	$159.85	$159.80
Purchase #5	$125.31	9.510%	$137.227	$137.23	$137.25	$137.20
Purchase #6	$141.87	3.396%	$146.6879	$146.69	$146.70	$146.70
Purchase #7	$66.31	6.630%	$70.7064	$70.71	$70.70	$70.70
7 purchase totals =	$971.32		$1,030.2048	$1,030.22	$1,030.25	$1,030.20