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	$45.43	3.211%	$46.8888	$46.89	$46.90	$46.90
Purchase #2	$111.64	12.734%	$125.8562	$125.86	$125.85	$125.90
Purchase #3	$29.37	7.655%	$31.6183	$31.62	$31.60	$31.60
Purchase #4	$169.35	12.451%	$190.4358	$190.44	$190.45	$190.40
Purchase #5	$134.39	8.821%	$146.2445	$146.24	$146.25	$146.20
Purchase #6	$35.39	5.689%	$37.4033	$37.40	$37.40	$37.40
Purchase #7	$124.60	5.800%	$131.8268	$131.83	$131.85	$131.80
7 purchase totals =	$650.17		$710.2737	$710.28	$710.30	$710.20