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	$183.99	4.133%	$191.5943	$191.59	$191.60	$191.60
Purchase #2	$158.31	5.644%	$167.245	$167.25	$167.25	$167.20
Purchase #3	$59.50	7.842%	$64.166	$64.17	$64.15	$64.20
Purchase #4	$244.67	6.570%	$260.7448	$260.74	$260.75	$260.70
Purchase #5	$35.78	12.605%	$40.2901	$40.29	$40.30	$40.30
Purchase #6	$76.60	12.132%	$85.8931	$85.89	$85.90	$85.90
Purchase #7	$117.49	8.623%	$127.6212	$127.62	$127.60	$127.60
7 purchase totals =	$876.34		$937.5545	$937.55	$937.55	$937.50