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	$45.38	11.840%	$50.753	$50.75	$50.75	$50.80
Purchase #2	$209.88	6.208%	$222.9094	$222.91	$222.90	$222.90
Purchase #3	$64.51	8.554%	$70.0282	$70.03	$70.05	$70.00
Purchase #4	$87.79	13.476%	$99.6206	$99.62	$99.60	$99.60
Purchase #5	$50.63	6.600%	$53.9716	$53.97	$53.95	$54.00
Purchase #6	$78.25	7.197%	$83.8817	$83.88	$83.90	$83.90
Purchase #7	$132.79	12.118%	$148.8815	$148.88	$148.90	$148.90
7 purchase totals =	$669.23		$730.0460	$730.04	$730.05	$730.10