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	$248.44	13.345%	$281.5943	$281.59	$281.60	$281.60
Purchase #2	$193.43	3.339%	$199.8886	$199.89	$199.90	$199.90
Purchase #3	$130.29	13.548%	$147.9417	$147.94	$147.95	$147.90
Purchase #4	$244.95	4.306%	$255.4975	$255.50	$255.50	$255.50
Purchase #5	$65.48	10.103%	$72.0954	$72.10	$72.10	$72.10
Purchase #6	$216.40	5.864%	$229.0897	$229.09	$229.10	$229.10
Purchase #7	$54.56	4.199%	$56.851	$56.85	$56.85	$56.90
7 purchase totals =	$1,153.55		$1,242.9582	$1,242.96	$1,243.00	$1,243.00