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	$218.37	3.196%	$225.3491	$225.35	$225.35	$225.30
Purchase #2	$50.89	11.814%	$56.9021	$56.90	$56.90	$56.90
Purchase #3	$139.79	10.562%	$154.5546	$154.55	$154.55	$154.60
Purchase #4	$40.69	10.108%	$44.8029	$44.80	$44.80	$44.80
Purchase #5	$52.85	12.672%	$59.5472	$59.55	$59.55	$59.50
Purchase #6	$180.29	9.527%	$197.4662	$197.47	$197.45	$197.50
Purchase #7	$18.94	9.556%	$20.7499	$20.75	$20.75	$20.70
7 purchase totals =	$701.82		$759.3720	$759.37	$759.35	$759.30