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	$75.90	12.822%	$85.6319	$85.63	$85.65	$85.60
Purchase #2	$53.85	13.128%	$60.9194	$60.92	$60.90	$60.90
Purchase #3	$74.76	11.449%	$83.3193	$83.32	$83.30	$83.30
Purchase #4	$108.62	12.221%	$121.8945	$121.89	$121.90	$121.90
Purchase #5	$143.25	3.614%	$148.4271	$148.43	$148.45	$148.40
Purchase #6	$26.29	3.167%	$27.1226	$27.12	$27.10	$27.10
Purchase #7	$86.39	4.855%	$90.5842	$90.58	$90.60	$90.60
7 purchase totals =	$569.06		$617.8990	$617.89	$617.90	$617.80