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	$79.60	11.698%	$88.9116	$88.91	$88.90	$88.90
Purchase #2	$26.53	12.800%	$29.9258	$29.93	$29.95	$29.90
Purchase #3	$161.37	8.455%	$175.0138	$175.01	$175.00	$175.00
Purchase #4	$52.75	13.657%	$59.9541	$59.95	$59.95	$60.00
Purchase #5	$50.66	12.287%	$56.8846	$56.88	$56.90	$56.90
Purchase #6	$64.80	11.816%	$72.4568	$72.46	$72.45	$72.50
Purchase #7	$25.68	5.257%	$27.03	$27.03	$27.05	$27.00
7 purchase totals =	$461.39		$510.1767	$510.17	$510.20	$510.20