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	$159.38	8.414%	$172.7902	$172.79	$172.80	$172.80
Purchase #2	$87.52	10.870%	$97.0334	$97.03	$97.05	$97.00
Purchase #3	$141.53	7.821%	$152.5991	$152.60	$152.60	$152.60
Purchase #4	$18.73	7.665%	$20.1657	$20.17	$20.15	$20.20
Purchase #5	$87.30	8.497%	$94.7179	$94.72	$94.70	$94.70
Purchase #6	$7.30	6.801%	$7.7965	$7.80	$7.80	$7.80
Purchase #7	$156.89	5.197%	$165.0436	$165.04	$165.05	$165.00
7 purchase totals =	$658.65		$710.1464	$710.15	$710.15	$710.10