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	$121.67	7.837%	$131.2053	$131.21	$131.20	$131.20
Purchase #2	$83.40	10.760%	$92.3738	$92.37	$92.35	$92.40
Purchase #3	$90.94	9.381%	$99.4711	$99.47	$99.45	$99.50
Purchase #4	$34.69	11.802%	$38.7841	$38.78	$38.80	$38.80
Purchase #5	$203.61	6.812%	$217.4799	$217.48	$217.50	$217.50
Purchase #6	$133.50	7.802%	$143.9157	$143.92	$143.90	$143.90
Purchase #7	$198.58	5.260%	$209.0253	$209.03	$209.05	$209.00
7 purchase totals =	$866.39		$932.2552	$932.26	$932.25	$932.30