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	$172.55	4.672%	$180.6115	$180.61	$180.60	$180.60
Purchase #2	$214.94	3.595%	$222.6671	$222.67	$222.65	$222.70
Purchase #3	$28.83	9.313%	$31.5149	$31.51	$31.50	$31.50
Purchase #4	$108.92	13.579%	$123.7102	$123.71	$123.70	$123.70
Purchase #5	$7.40	12.519%	$8.3264	$8.33	$8.35	$8.30
Purchase #6	$23.60	9.604%	$25.8665	$25.87	$25.85	$25.90
Purchase #7	$146.53	13.231%	$165.9174	$165.92	$165.90	$165.90
7 purchase totals =	$702.77		$758.6140	$758.62	$758.55	$758.60