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	$206.47	7.378%	$221.7034	$221.70	$221.70	$221.70
Purchase #2	$28.44	12.116%	$31.8858	$31.89	$31.90	$31.90
Purchase #3	$45.80	8.702%	$49.7855	$49.79	$49.80	$49.80
Purchase #4	$180.73	4.358%	$188.6062	$188.61	$188.60	$188.60
Purchase #5	$129.39	13.771%	$147.2083	$147.21	$147.20	$147.20
Purchase #6	$239.82	6.492%	$255.3891	$255.39	$255.40	$255.40
Purchase #7	$138.70	4.734%	$145.2661	$145.27	$145.25	$145.30
7 purchase totals =	$969.35		$1,039.8444	$1,039.86	$1,039.85	$1,039.90