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	$9.76	10.147%	$10.7503	$10.75	$10.75	$10.80
Purchase #2	$16.57	5.585%	$17.4954	$17.50	$17.50	$17.50
Purchase #3	$137.40	10.849%	$152.3065	$152.31	$152.30	$152.30
Purchase #4	$52.72	12.871%	$59.5056	$59.51	$59.50	$59.50
Purchase #5	$41.32	4.185%	$43.0492	$43.05	$43.05	$43.00
Purchase #6	$240.87	8.283%	$260.8213	$260.82	$260.80	$260.80
Purchase #7	$232.96	7.294%	$249.9521	$249.95	$249.95	$250.00
7 purchase totals =	$731.60		$793.8804	$793.89	$793.85	$793.90