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	$35.54	6.628%	$37.8956	$37.90	$37.90	$37.90
Purchase #2	$32.79	13.724%	$37.2901	$37.29	$37.30	$37.30
Purchase #3	$215.79	3.154%	$222.596	$222.60	$222.60	$222.60
Purchase #4	$93.41	13.306%	$105.8391	$105.84	$105.85	$105.80
Purchase #5	$190.98	6.267%	$202.9487	$202.95	$202.95	$202.90
Purchase #6	$217.65	7.105%	$233.114	$233.11	$233.10	$233.10
Purchase #7	$104.79	6.615%	$111.7219	$111.72	$111.70	$111.70
7 purchase totals =	$890.95		$951.4054	$951.41	$951.40	$951.30