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	$207.77	5.108%	$218.3829	$218.38	$218.40	$218.40
Purchase #2	$180.73	12.654%	$203.5996	$203.60	$203.60	$203.60
Purchase #3	$244.31	13.452%	$277.1746	$277.17	$277.15	$277.20
Purchase #4	$177.75	10.574%	$196.5453	$196.55	$196.55	$196.50
Purchase #5	$41.58	8.402%	$45.0736	$45.07	$45.05	$45.10
Purchase #6	$247.68	12.862%	$279.5366	$279.54	$279.55	$279.50
Purchase #7	$48.58	13.606%	$55.1898	$55.19	$55.20	$55.20
7 purchase totals =	$1,148.40		$1,275.5024	$1,275.50	$1,275.50	$1,275.50