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	$38.55	9.122%	$42.0665	$42.07	$42.05	$42.10
Purchase #2	$95.73	5.262%	$100.7673	$100.77	$100.75	$100.80
Purchase #3	$134.65	6.821%	$143.8345	$143.83	$143.85	$143.80
Purchase #4	$72.72	5.569%	$76.7698	$76.77	$76.75	$76.80
Purchase #5	$208.59	13.638%	$237.0375	$237.04	$237.05	$237.00
Purchase #6	$64.74	4.422%	$67.6028	$67.60	$67.60	$67.60
Purchase #7	$209.59	3.519%	$216.9655	$216.97	$216.95	$217.00
7 purchase totals =	$824.57		$885.0439	$885.05	$885.00	$885.10