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	$125.48	13.737%	$142.7172	$142.72	$142.70	$142.70
Purchase #2	$68.65	5.409%	$72.3633	$72.36	$72.35	$72.40
Purchase #3	$121.25	13.117%	$137.1544	$137.15	$137.15	$137.20
Purchase #4	$88.80	12.171%	$99.6078	$99.61	$99.60	$99.60
Purchase #5	$87.83	8.384%	$95.1937	$95.19	$95.20	$95.20
Purchase #6	$103.50	3.189%	$106.8006	$106.80	$106.80	$106.80
Purchase #7	$167.81	7.564%	$180.5031	$180.50	$180.50	$180.50
7 purchase totals =	$763.32		$834.3401	$834.33	$834.30	$834.40