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	$248.72	9.874%	$273.2786	$273.28	$273.30	$273.30
Purchase #2	$246.37	8.712%	$267.8338	$267.83	$267.85	$267.80
Purchase #3	$135.69	11.569%	$151.388	$151.39	$151.40	$151.40
Purchase #4	$247.34	10.847%	$274.169	$274.17	$274.15	$274.20
Purchase #5	$38.65	9.193%	$42.2031	$42.20	$42.20	$42.20
Purchase #6	$203.58	10.428%	$224.8093	$224.81	$224.80	$224.80
Purchase #7	$88.53	13.625%	$100.5922	$100.59	$100.60	$100.60
7 purchase totals =	$1,208.88		$1,334.2740	$1,334.27	$1,334.30	$1,334.30