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	$37.95	6.664%	$40.479	$40.48	$40.50	$40.50
Purchase #2	$132.95	9.256%	$145.2559	$145.26	$145.25	$145.30
Purchase #3	$123.84	5.694%	$130.8914	$130.89	$130.90	$130.90
Purchase #4	$221.90	12.680%	$250.0369	$250.04	$250.05	$250.00
Purchase #5	$159.71	13.155%	$180.7199	$180.72	$180.70	$180.70
Purchase #6	$233.82	5.226%	$246.0394	$246.04	$246.05	$246.00
Purchase #7	$161.65	4.839%	$169.4722	$169.47	$169.45	$169.50
7 purchase totals =	$1,071.82		$1,162.8947	$1,162.90	$1,162.90	$1,162.90