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	$66.46	9.712%	$72.9146	$72.91	$72.90	$72.90
Purchase #2	$35.66	13.369%	$40.4274	$40.43	$40.45	$40.40
Purchase #3	$5.35	6.311%	$5.6876	$5.69	$5.70	$5.70
Purchase #4	$200.81	8.352%	$217.5817	$217.58	$217.60	$217.60
Purchase #5	$218.66	11.419%	$243.6288	$243.63	$243.65	$243.60
Purchase #6	$63.26	3.559%	$65.5114	$65.51	$65.50	$65.50
Purchase #7	$189.40	7.627%	$203.8455	$203.85	$203.85	$203.80
7 purchase totals =	$779.60		$849.5970	$849.60	$849.65	$849.50