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	$135.47	13.161%	$153.2992	$153.30	$153.30	$153.30
Purchase #2	$157.50	13.678%	$179.0429	$179.04	$179.05	$179.00
Purchase #3	$148.34	11.787%	$165.8248	$165.82	$165.80	$165.80
Purchase #4	$250.47	5.737%	$264.8395	$264.84	$264.85	$264.80
Purchase #5	$51.84	3.602%	$53.7073	$53.71	$53.70	$53.70
Purchase #6	$118.63	10.637%	$131.2487	$131.25	$131.25	$131.20
Purchase #7	$197.35	3.631%	$204.5158	$204.52	$204.50	$204.50
7 purchase totals =	$1,059.60		$1,152.4782	$1,152.48	$1,152.45	$1,152.30