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	$136.92	10.287%	$151.005	$151.01	$151.00	$151.00
Purchase #2	$53.47	12.260%	$60.0254	$60.03	$60.05	$60.00
Purchase #3	$199.60	10.706%	$220.9692	$220.97	$220.95	$221.00
Purchase #4	$65.37	3.382%	$67.5808	$67.58	$67.60	$67.60
Purchase #5	$133.28	5.560%	$140.6904	$140.69	$140.70	$140.70
Purchase #6	$33.35	13.606%	$37.8876	$37.89	$37.90	$37.90
Purchase #7	$151.67	4.345%	$158.2601	$158.26	$158.25	$158.30
7 purchase totals =	$773.66		$836.4185	$836.43	$836.45	$836.50