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	$37.93	12.390%	$42.6295	$42.63	$42.65	$42.60
Purchase #2	$211.93	12.674%	$238.79	$238.79	$238.80	$238.80
Purchase #3	$178.58	6.180%	$189.6162	$189.62	$189.60	$189.60
Purchase #4	$248.77	6.411%	$264.7186	$264.72	$264.70	$264.70
Purchase #5	$33.89	8.628%	$36.814	$36.81	$36.80	$36.80
Purchase #6	$165.28	10.439%	$182.5336	$182.53	$182.55	$182.50
Purchase #7	$80.31	10.194%	$88.4968	$88.50	$88.50	$88.50
7 purchase totals =	$956.69		$1,043.5987	$1,043.60	$1,043.60	$1,043.50