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	$151.83	13.167%	$171.8215	$171.82	$171.80	$171.80
Purchase #2	$16.85	8.274%	$18.2442	$18.24	$18.25	$18.20
Purchase #3	$15.33	7.823%	$16.5293	$16.53	$16.55	$16.50
Purchase #4	$82.55	11.742%	$92.243	$92.24	$92.25	$92.20
Purchase #5	$64.61	10.313%	$71.2732	$71.27	$71.25	$71.30
Purchase #6	$73.29	12.392%	$82.3721	$82.37	$82.35	$82.40
Purchase #7	$46.79	13.385%	$53.0528	$53.05	$53.05	$53.10
7 purchase totals =	$451.25		$505.5361	$505.52	$505.50	$505.50