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	$10.90	10.224%	$12.0144	$12.01	$12.00	$12.00
Purchase #2	$33.96	4.477%	$35.4804	$35.48	$35.50	$35.50
Purchase #3	$151.96	13.586%	$172.6053	$172.61	$172.60	$172.60
Purchase #4	$219.66	10.621%	$242.9901	$242.99	$243.00	$243.00
Purchase #5	$186.59	11.540%	$208.1225	$208.12	$208.10	$208.10
Purchase #6	$76.85	6.762%	$82.0466	$82.05	$82.05	$82.00
Purchase #7	$120.89	8.576%	$131.2575	$131.26	$131.25	$131.30
7 purchase totals =	$800.81		$884.5168	$884.52	$884.50	$884.50