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	$12.96	7.104%	$13.8807	$13.88	$13.90	$13.90
Purchase #2	$40.69	4.635%	$42.576	$42.58	$42.60	$42.60
Purchase #3	$7.38	7.110%	$7.9047	$7.90	$7.90	$7.90
Purchase #4	$249.47	12.721%	$281.2051	$281.21	$281.20	$281.20
Purchase #5	$227.26	3.862%	$236.0368	$236.04	$236.05	$236.00
Purchase #6	$35.58	13.792%	$40.4872	$40.49	$40.50	$40.50
Purchase #7	$237.82	11.114%	$264.2513	$264.25	$264.25	$264.30
7 purchase totals =	$811.16		$886.3418	$886.35	$886.40	$886.40