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	$164.68	12.659%	$185.5268	$185.53	$185.55	$185.50
Purchase #2	$182.55	9.770%	$200.3851	$200.39	$200.40	$200.40
Purchase #3	$151.72	5.126%	$159.4972	$159.50	$159.50	$159.50
Purchase #4	$127.85	6.267%	$135.8624	$135.86	$135.85	$135.90
Purchase #5	$47.46	7.343%	$50.945	$50.95	$50.95	$50.90
Purchase #6	$20.48	6.425%	$21.7958	$21.80	$21.80	$21.80
Purchase #7	$43.27	10.221%	$47.6926	$47.69	$47.70	$47.70
7 purchase totals =	$738.01		$801.7049	$801.72	$801.75	$801.70