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	$209.81	7.487%	$225.5185	$225.52	$225.50	$225.50
Purchase #2	$29.31	6.737%	$31.2846	$31.28	$31.30	$31.30
Purchase #3	$132.57	10.771%	$146.8491	$146.85	$146.85	$146.80
Purchase #4	$234.34	5.384%	$246.9569	$246.96	$246.95	$247.00
Purchase #5	$81.26	11.632%	$90.7122	$90.71	$90.70	$90.70
Purchase #6	$130.28	9.177%	$142.2358	$142.24	$142.25	$142.20
Purchase #7	$32.91	7.242%	$35.2933	$35.29	$35.30	$35.30
7 purchase totals =	$850.48		$918.8504	$918.85	$918.85	$918.80