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	$210.36	6.318%	$223.6505	$223.65	$223.65	$223.70
Purchase #2	$16.46	9.485%	$18.0212	$18.02	$18.00	$18.00
Purchase #3	$94.25	6.723%	$100.5864	$100.59	$100.60	$100.60
Purchase #4	$160.62	12.208%	$180.2285	$180.23	$180.25	$180.20
Purchase #5	$31.33	8.136%	$33.879	$33.88	$33.90	$33.90
Purchase #6	$131.93	6.466%	$140.4606	$140.46	$140.45	$140.50
Purchase #7	$94.30	12.771%	$106.3431	$106.34	$106.35	$106.30
7 purchase totals =	$739.25		$803.1693	$803.17	$803.20	$803.20