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	$80.69	12.289%	$90.606	$90.61	$90.60	$90.60
Purchase #2	$248.44	11.334%	$276.5982	$276.60	$276.60	$276.60
Purchase #3	$117.29	3.317%	$121.1805	$121.18	$121.20	$121.20
Purchase #4	$32.60	4.494%	$34.065	$34.07	$34.05	$34.10
Purchase #5	$216.56	10.230%	$238.7141	$238.71	$238.70	$238.70
Purchase #6	$145.48	4.420%	$151.9102	$151.91	$151.90	$151.90
Purchase #7	$74.54	8.505%	$80.8796	$80.88	$80.90	$80.90
7 purchase totals =	$915.60		$993.9536	$993.96	$993.95	$994.00