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	$45.64	8.492%	$49.5157	$49.52	$49.50	$49.50
Purchase #2	$130.63	10.580%	$144.4507	$144.45	$144.45	$144.50
Purchase #3	$64.95	3.400%	$67.1583	$67.16	$67.15	$67.20
Purchase #4	$26.69	11.172%	$29.6718	$29.67	$29.65	$29.70
Purchase #5	$30.58	6.637%	$32.6096	$32.61	$32.60	$32.60
Purchase #6	$66.89	13.639%	$76.0131	$76.01	$76.00	$76.00
Purchase #7	$134.58	11.851%	$150.5291	$150.53	$150.55	$150.50
7 purchase totals =	$499.96		$549.9483	$549.95	$549.90	$550.00