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	$181.66	12.442%	$204.2621	$204.26	$204.25	$204.30
Purchase #2	$233.89	10.870%	$259.3138	$259.31	$259.30	$259.30
Purchase #3	$95.31	8.796%	$103.6935	$103.69	$103.70	$103.70
Purchase #4	$159.34	5.749%	$168.5005	$168.50	$168.50	$168.50
Purchase #5	$128.60	11.824%	$143.8057	$143.81	$143.80	$143.80
Purchase #6	$200.32	12.709%	$225.7787	$225.78	$225.80	$225.80
Purchase #7	$180.95	13.370%	$205.143	$205.14	$205.15	$205.10
7 purchase totals =	$1,180.07		$1,310.4973	$1,310.49	$1,310.50	$1,310.50