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	$36.56	7.204%	$39.1938	$39.19	$39.20	$39.20
Purchase #2	$142.76	5.799%	$151.0387	$151.04	$151.05	$151.00
Purchase #3	$143.60	8.511%	$155.8218	$155.82	$155.80	$155.80
Purchase #4	$244.63	5.807%	$258.8357	$258.84	$258.85	$258.80
Purchase #5	$52.67	7.196%	$56.4601	$56.46	$56.45	$56.50
Purchase #6	$128.37	12.639%	$144.5947	$144.59	$144.60	$144.60
Purchase #7	$137.47	6.416%	$146.2901	$146.29	$146.30	$146.30
7 purchase totals =	$886.06		$952.2349	$952.23	$952.25	$952.20