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	$52.37	6.628%	$55.8411	$55.84	$55.85	$55.80
Purchase #2	$202.43	10.283%	$223.2459	$223.25	$223.25	$223.20
Purchase #3	$126.56	4.186%	$131.8578	$131.86	$131.85	$131.90
Purchase #4	$10.65	13.643%	$12.103	$12.10	$12.10	$12.10
Purchase #5	$148.85	10.487%	$164.4599	$164.46	$164.45	$164.50
Purchase #6	$203.69	3.548%	$210.9169	$210.92	$210.90	$210.90
Purchase #7	$33.31	10.581%	$36.8345	$36.83	$36.85	$36.80
7 purchase totals =	$777.86		$835.2591	$835.26	$835.25	$835.20