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	$117.38	12.606%	$132.1769	$132.18	$132.20	$132.20
Purchase #2	$196.32	13.132%	$222.1007	$222.10	$222.10	$222.10
Purchase #3	$82.47	3.646%	$85.4769	$85.48	$85.50	$85.50
Purchase #4	$156.47	10.591%	$173.0417	$173.04	$173.05	$173.00
Purchase #5	$141.72	7.407%	$152.2172	$152.22	$152.20	$152.20
Purchase #6	$12.80	3.300%	$13.2224	$13.22	$13.20	$13.20
Purchase #7	$19.71	13.416%	$22.3543	$22.35	$22.35	$22.40
7 purchase totals =	$726.87		$800.5901	$800.59	$800.60	$800.60