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	$34.73	11.312%	$38.6587	$38.66	$38.65	$38.70
Purchase #2	$122.35	6.295%	$130.0519	$130.05	$130.05	$130.10
Purchase #3	$85.38	7.576%	$91.8484	$91.85	$91.85	$91.80
Purchase #4	$74.89	8.735%	$81.4316	$81.43	$81.45	$81.40
Purchase #5	$38.72	3.816%	$40.1976	$40.20	$40.20	$40.20
Purchase #6	$238.69	7.140%	$255.7325	$255.73	$255.75	$255.70
Purchase #7	$71.34	9.413%	$78.0552	$78.06	$78.05	$78.10
7 purchase totals =	$666.10		$715.9759	$715.98	$716.00	$716.00