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	$6.73	9.864%	$7.3938	$7.39	$7.40	$7.40
Purchase #2	$143.61	3.560%	$148.7225	$148.72	$148.70	$148.70
Purchase #3	$38.66	7.227%	$41.454	$41.45	$41.45	$41.50
Purchase #4	$31.82	13.790%	$36.208	$36.21	$36.20	$36.20
Purchase #5	$146.39	6.681%	$156.1703	$156.17	$156.15	$156.20
Purchase #6	$176.74	7.818%	$190.5575	$190.56	$190.55	$190.60
Purchase #7	$152.51	3.755%	$158.2368	$158.24	$158.25	$158.20
7 purchase totals =	$696.46		$738.7429	$738.74	$738.70	$738.80