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	$241.29	12.161%	$270.6333	$270.63	$270.65	$270.60
Purchase #2	$66.47	8.240%	$71.9471	$71.95	$71.95	$71.90
Purchase #3	$127.46	5.686%	$134.7074	$134.71	$134.70	$134.70
Purchase #4	$38.87	10.330%	$42.8853	$42.89	$42.90	$42.90
Purchase #5	$38.46	10.852%	$42.6337	$42.63	$42.65	$42.60
Purchase #6	$77.31	8.313%	$83.7368	$83.74	$83.75	$83.70
Purchase #7	$214.98	4.217%	$224.0457	$224.05	$224.05	$224.00
7 purchase totals =	$804.84		$870.5893	$870.60	$870.65	$870.40