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	$113.36	13.373%	$128.5196	$128.52	$128.50	$128.50
Purchase #2	$235.57	13.351%	$267.021	$267.02	$267.00	$267.00
Purchase #3	$23.91	5.304%	$25.1782	$25.18	$25.20	$25.20
Purchase #4	$87.88	4.742%	$92.0473	$92.05	$92.05	$92.00
Purchase #5	$9.76	11.693%	$10.9012	$10.90	$10.90	$10.90
Purchase #6	$196.90	13.659%	$223.7946	$223.79	$223.80	$223.80
Purchase #7	$100.25	11.491%	$111.7697	$111.77	$111.75	$111.80
7 purchase totals =	$767.63		$859.2316	$859.23	$859.20	$859.20