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	$243.63	4.594%	$254.8224	$254.82	$254.80	$254.80
Purchase #2	$52.80	6.290%	$56.1211	$56.12	$56.10	$56.10
Purchase #3	$60.61	9.666%	$66.4686	$66.47	$66.45	$66.50
Purchase #4	$75.94	3.847%	$78.8614	$78.86	$78.85	$78.90
Purchase #5	$208.68	6.251%	$221.7246	$221.72	$221.70	$221.70
Purchase #6	$61.49	3.525%	$63.6575	$63.66	$63.65	$63.70
Purchase #7	$78.86	10.238%	$86.9337	$86.93	$86.95	$86.90
7 purchase totals =	$782.01		$828.5893	$828.58	$828.50	$828.60