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	$50.27	11.136%	$55.8681	$55.87	$55.85	$55.90
Purchase #2	$207.86	8.444%	$225.4117	$225.41	$225.40	$225.40
Purchase #3	$191.95	13.826%	$218.489	$218.49	$218.50	$218.50
Purchase #4	$43.84	3.628%	$45.4305	$45.43	$45.45	$45.40
Purchase #5	$44.57	9.718%	$48.9013	$48.90	$48.90	$48.90
Purchase #6	$133.40	11.186%	$148.3221	$148.32	$148.30	$148.30
Purchase #7	$83.68	11.303%	$93.1384	$93.14	$93.15	$93.10
7 purchase totals =	$755.57		$835.5611	$835.56	$835.55	$835.50