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	$63.61	12.325%	$71.4499	$71.45	$71.45	$71.40
Purchase #2	$220.45	11.380%	$245.5372	$245.54	$245.55	$245.50
Purchase #3	$120.71	8.645%	$131.1454	$131.15	$131.15	$131.10
Purchase #4	$37.47	12.161%	$42.0267	$42.03	$42.05	$42.00
Purchase #5	$55.81	10.804%	$61.8397	$61.84	$61.85	$61.80
Purchase #6	$30.63	6.626%	$32.6595	$32.66	$32.65	$32.70
Purchase #7	$20.30	9.128%	$22.153	$22.15	$22.15	$22.20
7 purchase totals =	$548.98		$606.8114	$606.82	$606.85	$606.70