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	$42.71	6.517%	$45.4934	$45.49	$45.50	$45.50
Purchase #2	$77.50	11.806%	$86.6497	$86.65	$86.65	$86.60
Purchase #3	$213.83	10.554%	$236.3976	$236.40	$236.40	$236.40
Purchase #4	$88.70	10.169%	$97.7199	$97.72	$97.70	$97.70
Purchase #5	$113.67	4.675%	$118.9841	$118.98	$119.00	$119.00
Purchase #6	$65.47	9.164%	$71.4697	$71.47	$71.45	$71.50
Purchase #7	$128.40	8.616%	$139.4629	$139.46	$139.45	$139.50
7 purchase totals =	$730.28		$796.1773	$796.17	$796.15	$796.20