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	$93.61	12.400%	$105.2176	$105.22	$105.20	$105.20
Purchase #2	$121.91	5.110%	$128.1396	$128.14	$128.15	$128.10
Purchase #3	$74.31	3.497%	$76.9086	$76.91	$76.90	$76.90
Purchase #4	$151.94	8.821%	$165.3426	$165.34	$165.35	$165.30
Purchase #5	$43.59	13.401%	$49.4315	$49.43	$49.45	$49.40
Purchase #6	$22.50	13.497%	$25.5368	$25.54	$25.55	$25.50
Purchase #7	$229.93	10.235%	$253.4633	$253.46	$253.45	$253.50
7 purchase totals =	$737.79		$804.0400	$804.04	$804.05	$803.90