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	$123.50	11.388%	$137.5642	$137.56	$137.55	$137.60
Purchase #2	$42.27	4.809%	$44.3028	$44.30	$44.30	$44.30
Purchase #3	$101.29	10.226%	$111.6479	$111.65	$111.65	$111.60
Purchase #4	$151.28	13.315%	$171.4229	$171.42	$171.40	$171.40
Purchase #5	$156.84	8.362%	$169.955	$169.96	$169.95	$170.00
Purchase #6	$124.34	9.806%	$136.5328	$136.53	$136.55	$136.50
Purchase #7	$48.31	12.595%	$54.3946	$54.39	$54.40	$54.40
7 purchase totals =	$747.83		$825.8202	$825.81	$825.80	$825.80