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	$126.56	8.694%	$137.5631	$137.56	$137.55	$137.60
Purchase #2	$169.48	13.488%	$192.3395	$192.34	$192.35	$192.30
Purchase #3	$102.73	13.871%	$116.9797	$116.98	$117.00	$117.00
Purchase #4	$147.37	12.457%	$165.7279	$165.73	$165.75	$165.70
Purchase #5	$128.55	9.728%	$141.0553	$141.06	$141.05	$141.10
Purchase #6	$95.48	5.787%	$101.0054	$101.01	$101.00	$101.00
Purchase #7	$114.25	12.724%	$128.7872	$128.79	$128.80	$128.80
7 purchase totals =	$884.42		$983.4581	$983.47	$983.50	$983.50