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	$48.49	4.287%	$50.5688	$50.57	$50.55	$50.60
Purchase #2	$182.89	12.221%	$205.241	$205.24	$205.25	$205.20
Purchase #3	$123.98	11.257%	$137.9364	$137.94	$137.95	$137.90
Purchase #4	$28.65	4.194%	$29.8516	$29.85	$29.85	$29.90
Purchase #5	$59.80	13.439%	$67.8365	$67.84	$67.85	$67.80
Purchase #6	$151.25	5.483%	$159.543	$159.54	$159.55	$159.50
Purchase #7	$160.43	9.466%	$175.6163	$175.62	$175.60	$175.60
7 purchase totals =	$755.49		$826.5936	$826.60	$826.60	$826.50