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	$135.37	6.277%	$143.8672	$143.87	$143.85	$143.90
Purchase #2	$166.66	3.480%	$172.4598	$172.46	$172.45	$172.50
Purchase #3	$79.83	9.322%	$87.2718	$87.27	$87.25	$87.30
Purchase #4	$68.83	10.605%	$76.1294	$76.13	$76.15	$76.10
Purchase #5	$159.52	7.223%	$171.0421	$171.04	$171.05	$171.00
Purchase #6	$60.95	10.299%	$67.2272	$67.23	$67.25	$67.20
Purchase #7	$78.45	8.823%	$85.3716	$85.37	$85.35	$85.40
7 purchase totals =	$749.61		$803.3691	$803.37	$803.35	$803.40