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	$46.90	11.741%	$52.4065	$52.41	$52.40	$52.40
Purchase #2	$139.47	11.496%	$155.5035	$155.50	$155.50	$155.50
Purchase #3	$15.86	10.628%	$17.5456	$17.55	$17.55	$17.50
Purchase #4	$122.65	11.771%	$137.0871	$137.09	$137.10	$137.10
Purchase #5	$175.44	8.557%	$190.4524	$190.45	$190.45	$190.50
Purchase #6	$59.56	12.517%	$67.0151	$67.02	$67.00	$67.00
Purchase #7	$158.69	13.294%	$179.7862	$179.79	$179.80	$179.80
7 purchase totals =	$718.57		$799.7964	$799.81	$799.80	$799.80