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	$189.71	12.698%	$213.7994	$213.80	$213.80	$213.80
Purchase #2	$149.50	10.673%	$165.4561	$165.46	$165.45	$165.50
Purchase #3	$86.94	10.407%	$95.9878	$95.99	$96.00	$96.00
Purchase #4	$78.71	8.297%	$85.2406	$85.24	$85.25	$85.20
Purchase #5	$185.82	7.593%	$199.9293	$199.93	$199.95	$199.90
Purchase #6	$55.66	6.682%	$59.3792	$59.38	$59.40	$59.40
Purchase #7	$88.58	6.793%	$94.5972	$94.60	$94.60	$94.60
7 purchase totals =	$834.92		$914.3896	$914.40	$914.45	$914.40