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	$53.88	6.358%	$57.3057	$57.31	$57.30	$57.30
Purchase #2	$122.94	11.858%	$137.5182	$137.52	$137.50	$137.50
Purchase #3	$247.79	8.268%	$268.2773	$268.28	$268.30	$268.30
Purchase #4	$147.45	11.461%	$164.3492	$164.35	$164.35	$164.30
Purchase #5	$154.86	10.674%	$171.3898	$171.39	$171.40	$171.40
Purchase #6	$41.48	11.306%	$46.1697	$46.17	$46.15	$46.20
Purchase #7	$146.52	3.699%	$151.9398	$151.94	$151.95	$151.90
7 purchase totals =	$914.92		$996.9497	$996.96	$996.95	$996.90