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	$206.61	4.216%	$215.3207	$215.32	$215.30	$215.30
Purchase #2	$200.90	10.788%	$222.5731	$222.57	$222.55	$222.60
Purchase #3	$160.35	8.239%	$173.5612	$173.56	$173.55	$173.60
Purchase #4	$31.25	10.340%	$34.4813	$34.48	$34.50	$34.50
Purchase #5	$163.27	7.162%	$174.9634	$174.96	$174.95	$175.00
Purchase #6	$48.66	8.595%	$52.8423	$52.84	$52.85	$52.80
Purchase #7	$55.57	6.345%	$59.0959	$59.10	$59.10	$59.10
7 purchase totals =	$866.61		$932.8379	$932.83	$932.80	$932.90