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	$90.67	4.221%	$94.4972	$94.50	$94.50	$94.50
Purchase #2	$11.52	9.467%	$12.6106	$12.61	$12.60	$12.60
Purchase #3	$45.79	9.655%	$50.211	$50.21	$50.20	$50.20
Purchase #4	$16.34	5.479%	$17.2353	$17.24	$17.25	$17.20
Purchase #5	$65.81	9.531%	$72.0824	$72.08	$72.10	$72.10
Purchase #6	$71.46	10.330%	$78.8418	$78.84	$78.85	$78.80
Purchase #7	$197.85	12.738%	$223.0521	$223.05	$223.05	$223.10
7 purchase totals =	$499.44		$548.5304	$548.53	$548.55	$548.50