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	$27.69	12.828%	$31.2421	$31.24	$31.25	$31.20
Purchase #2	$229.84	13.157%	$260.08	$260.08	$260.10	$260.10
Purchase #3	$140.89	7.510%	$151.4708	$151.47	$151.45	$151.50
Purchase #4	$117.48	11.522%	$131.016	$131.02	$131.00	$131.00
Purchase #5	$6.61	9.375%	$7.2297	$7.23	$7.25	$7.20
Purchase #6	$67.38	5.775%	$71.2712	$71.27	$71.25	$71.30
Purchase #7	$147.70	5.296%	$155.5222	$155.52	$155.50	$155.50
7 purchase totals =	$737.59		$807.8320	$807.83	$807.80	$807.80