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	$36.80	12.149%	$41.2708	$41.27	$41.25	$41.30
Purchase #2	$69.51	12.547%	$78.2314	$78.23	$78.25	$78.20
Purchase #3	$144.84	9.698%	$158.8866	$158.89	$158.90	$158.90
Purchase #4	$242.51	10.569%	$268.1409	$268.14	$268.15	$268.10
Purchase #5	$9.31	10.657%	$10.3022	$10.30	$10.30	$10.30
Purchase #6	$244.44	4.482%	$255.3958	$255.40	$255.40	$255.40
Purchase #7	$123.48	11.350%	$137.495	$137.50	$137.50	$137.50
7 purchase totals =	$870.89		$949.7227	$949.73	$949.75	$949.70