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	$71.57	9.311%	$78.2339	$78.23	$78.25	$78.20
Purchase #2	$167.50	10.142%	$184.4879	$184.49	$184.50	$184.50
Purchase #3	$128.83	13.760%	$146.557	$146.56	$146.55	$146.60
Purchase #4	$32.82	11.266%	$36.5175	$36.52	$36.50	$36.50
Purchase #5	$185.97	7.464%	$199.8508	$199.85	$199.85	$199.90
Purchase #6	$202.49	10.823%	$224.4055	$224.41	$224.40	$224.40
Purchase #7	$11.58	8.553%	$12.5704	$12.57	$12.55	$12.60
7 purchase totals =	$800.76		$882.6230	$882.63	$882.60	$882.70