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	$75.48	12.678%	$85.0494	$85.05	$85.05	$85.00
Purchase #2	$143.53	11.128%	$159.502	$159.50	$159.50	$159.50
Purchase #3	$43.79	12.428%	$49.2322	$49.23	$49.25	$49.20
Purchase #4	$82.39	12.432%	$92.6327	$92.63	$92.65	$92.60
Purchase #5	$11.43	13.111%	$12.9286	$12.93	$12.95	$12.90
Purchase #6	$211.76	4.860%	$222.0515	$222.05	$222.05	$222.10
Purchase #7	$42.77	3.862%	$44.4218	$44.42	$44.40	$44.40
7 purchase totals =	$611.15		$665.8182	$665.81	$665.85	$665.70