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	$39.78	7.105%	$42.6064	$42.61	$42.60	$42.60
Purchase #2	$89.85	13.791%	$102.2412	$102.24	$102.25	$102.20
Purchase #3	$105.70	10.772%	$117.086	$117.09	$117.10	$117.10
Purchase #4	$93.35	13.743%	$106.1791	$106.18	$106.20	$106.20
Purchase #5	$148.28	4.850%	$155.4716	$155.47	$155.45	$155.50
Purchase #6	$156.74	3.234%	$161.809	$161.81	$161.80	$161.80
Purchase #7	$226.78	13.157%	$256.6174	$256.62	$256.60	$256.60
7 purchase totals =	$860.48		$942.0107	$942.02	$942.00	$942.00