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	$122.77	11.163%	$136.4748	$136.47	$136.45	$136.50
Purchase #2	$68.94	13.210%	$78.047	$78.05	$78.05	$78.00
Purchase #3	$59.54	4.592%	$62.2741	$62.27	$62.25	$62.30
Purchase #4	$114.38	9.817%	$125.6087	$125.61	$125.60	$125.60
Purchase #5	$193.37	8.853%	$210.489	$210.49	$210.50	$210.50
Purchase #6	$218.49	11.449%	$243.5049	$243.50	$243.50	$243.50
Purchase #7	$29.62	12.176%	$33.2265	$33.23	$33.25	$33.20
7 purchase totals =	$807.11		$889.6250	$889.62	$889.60	$889.60