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	$11.76	3.356%	$12.1547	$12.15	$12.15	$12.20
Purchase #2	$35.76	11.395%	$39.8349	$39.83	$39.85	$39.80
Purchase #3	$86.28	11.849%	$96.5033	$96.50	$96.50	$96.50
Purchase #4	$119.95	6.770%	$128.0706	$128.07	$128.05	$128.10
Purchase #5	$48.73	7.763%	$52.5129	$52.51	$52.50	$52.50
Purchase #6	$123.32	6.626%	$131.4912	$131.49	$131.50	$131.50
Purchase #7	$19.47	9.746%	$21.3675	$21.37	$21.35	$21.40
7 purchase totals =	$445.27		$481.9351	$481.92	$481.90	$482.00