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	$227.84	12.147%	$255.5157	$255.52	$255.50	$255.50
Purchase #2	$148.51	5.640%	$156.886	$156.89	$156.90	$156.90
Purchase #3	$26.59	7.641%	$28.6217	$28.62	$28.60	$28.60
Purchase #4	$186.66	7.755%	$201.1355	$201.14	$201.15	$201.10
Purchase #5	$66.63	7.790%	$71.8205	$71.82	$71.80	$71.80
Purchase #6	$137.28	10.294%	$151.4116	$151.41	$151.40	$151.40
Purchase #7	$85.41	5.460%	$90.0734	$90.07	$90.05	$90.10
7 purchase totals =	$878.92		$955.4644	$955.47	$955.40	$955.40