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	$36.42	13.669%	$41.3982	$41.40	$41.40	$41.40
Purchase #2	$32.45	6.427%	$34.5356	$34.54	$34.55	$34.50
Purchase #3	$46.29	5.234%	$48.7128	$48.71	$48.70	$48.70
Purchase #4	$121.89	4.470%	$127.3385	$127.34	$127.35	$127.30
Purchase #5	$34.77	6.724%	$37.1079	$37.11	$37.10	$37.10
Purchase #6	$12.78	4.227%	$13.3202	$13.32	$13.30	$13.30
Purchase #7	$186.32	9.578%	$204.1657	$204.17	$204.15	$204.20
7 purchase totals =	$470.92		$506.5789	$506.59	$506.55	$506.50