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	$47.97	10.325%	$52.9229	$52.92	$52.90	$52.90
Purchase #2	$131.53	6.116%	$139.5744	$139.57	$139.55	$139.60
Purchase #3	$177.38	6.791%	$189.4259	$189.43	$189.45	$189.40
Purchase #4	$23.70	9.251%	$25.8925	$25.89	$25.90	$25.90
Purchase #5	$188.66	12.826%	$212.8575	$212.86	$212.85	$212.90
Purchase #6	$17.56	5.833%	$18.5843	$18.58	$18.60	$18.60
Purchase #7	$68.39	4.733%	$71.6269	$71.63	$71.65	$71.60
7 purchase totals =	$655.19		$710.8844	$710.88	$710.90	$710.90