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	$42.27	10.516%	$46.7151	$46.72	$46.70	$46.70
Purchase #2	$124.74	12.436%	$140.2527	$140.25	$140.25	$140.30
Purchase #3	$37.84	11.441%	$42.1693	$42.17	$42.15	$42.20
Purchase #4	$73.64	5.249%	$77.5054	$77.51	$77.50	$77.50
Purchase #5	$35.56	11.300%	$39.5783	$39.58	$39.60	$39.60
Purchase #6	$92.40	13.199%	$104.5959	$104.60	$104.60	$104.60
Purchase #7	$29.80	12.706%	$33.5864	$33.59	$33.60	$33.60
7 purchase totals =	$436.25		$484.4031	$484.42	$484.40	$484.50