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	$79.78	13.729%	$90.733	$90.73	$90.75	$90.70
Purchase #2	$177.58	10.814%	$196.7835	$196.78	$196.80	$196.80
Purchase #3	$88.63	7.778%	$95.5236	$95.52	$95.50	$95.50
Purchase #4	$46.49	13.436%	$52.7364	$52.74	$52.75	$52.70
Purchase #5	$180.26	4.693%	$188.7196	$188.72	$188.70	$188.70
Purchase #6	$79.34	7.626%	$85.3905	$85.39	$85.40	$85.40
Purchase #7	$140.65	12.320%	$157.9781	$157.98	$158.00	$158.00
7 purchase totals =	$792.73		$867.8647	$867.86	$867.90	$867.80