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	$36.30	11.418%	$40.4447	$40.44	$40.45	$40.40
Purchase #2	$161.48	6.742%	$172.367	$172.37	$172.35	$172.40
Purchase #3	$23.38	9.453%	$25.5901	$25.59	$25.60	$25.60
Purchase #4	$243.42	4.640%	$254.7147	$254.71	$254.70	$254.70
Purchase #5	$64.34	11.475%	$71.723	$71.72	$71.70	$71.70
Purchase #6	$235.63	3.309%	$243.427	$243.43	$243.45	$243.40
Purchase #7	$108.91	13.596%	$123.7174	$123.72	$123.70	$123.70
7 purchase totals =	$873.46		$931.9839	$931.98	$931.95	$931.90