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	$175.33	8.338%	$189.949	$189.95	$189.95	$189.90
Purchase #2	$124.78	5.799%	$132.016	$132.02	$132.00	$132.00
Purchase #3	$98.43	12.593%	$110.8253	$110.83	$110.85	$110.80
Purchase #4	$15.68	13.381%	$17.7781	$17.78	$17.80	$17.80
Purchase #5	$36.45	12.107%	$40.863	$40.86	$40.85	$40.90
Purchase #6	$82.39	9.678%	$90.3637	$90.36	$90.35	$90.40
Purchase #7	$37.50	9.762%	$41.1608	$41.16	$41.15	$41.20
7 purchase totals =	$570.56		$622.9559	$622.96	$622.95	$623.00