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	$129.53	13.325%	$146.7899	$146.79	$146.80	$146.80
Purchase #2	$126.36	4.864%	$132.5062	$132.51	$132.50	$132.50
Purchase #3	$40.27	5.656%	$42.5477	$42.55	$42.55	$42.50
Purchase #4	$116.52	13.651%	$132.4261	$132.43	$132.45	$132.40
Purchase #5	$62.76	9.779%	$68.8973	$68.90	$68.90	$68.90
Purchase #6	$168.97	9.762%	$185.4649	$185.46	$185.45	$185.50
Purchase #7	$124.46	4.546%	$130.118	$130.12	$130.10	$130.10
7 purchase totals =	$768.87		$838.7501	$838.76	$838.75	$838.70