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	$34.39	11.151%	$38.2248	$38.22	$38.20	$38.20
Purchase #2	$239.30	7.588%	$257.4581	$257.46	$257.45	$257.50
Purchase #3	$75.62	13.184%	$85.5897	$85.59	$85.60	$85.60
Purchase #4	$89.77	10.846%	$99.5065	$99.51	$99.50	$99.50
Purchase #5	$55.53	6.595%	$59.1922	$59.19	$59.20	$59.20
Purchase #6	$65.29	6.460%	$69.5077	$69.51	$69.50	$69.50
Purchase #7	$197.67	8.158%	$213.7959	$213.80	$213.80	$213.80
7 purchase totals =	$757.57		$823.2749	$823.28	$823.25	$823.30