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	$141.86	13.406%	$160.8778	$160.88	$160.90	$160.90
Purchase #2	$87.72	13.449%	$99.5175	$99.52	$99.50	$99.50
Purchase #3	$204.43	13.544%	$232.118	$232.12	$232.10	$232.10
Purchase #4	$40.71	13.732%	$46.3003	$46.30	$46.30	$46.30
Purchase #5	$28.34	10.103%	$31.2032	$31.20	$31.20	$31.20
Purchase #6	$128.89	8.383%	$139.6948	$139.69	$139.70	$139.70
Purchase #7	$7.34	5.231%	$7.724	$7.72	$7.70	$7.70
7 purchase totals =	$639.29		$717.4356	$717.43	$717.40	$717.40