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	$247.32	3.316%	$255.5211	$255.52	$255.50	$255.50
Purchase #2	$29.53	12.602%	$33.2514	$33.25	$33.25	$33.30
Purchase #3	$136.50	6.503%	$145.3766	$145.38	$145.40	$145.40
Purchase #4	$229.92	10.634%	$254.3697	$254.37	$254.35	$254.40
Purchase #5	$110.35	7.427%	$118.5457	$118.55	$118.55	$118.50
Purchase #6	$225.69	12.273%	$253.3889	$253.39	$253.40	$253.40
Purchase #7	$196.50	8.296%	$212.8016	$212.80	$212.80	$212.80
7 purchase totals =	$1,175.81		$1,273.2550	$1,273.26	$1,273.25	$1,273.30