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	$67.27	6.309%	$71.5141	$71.51	$71.50	$71.50
Purchase #2	$92.57	10.212%	$102.0232	$102.02	$102.00	$102.00
Purchase #3	$80.71	11.297%	$89.8278	$89.83	$89.85	$89.80
Purchase #4	$20.61	11.633%	$23.0076	$23.01	$23.00	$23.00
Purchase #5	$243.82	12.672%	$274.7169	$274.72	$274.70	$274.70
Purchase #6	$45.88	9.588%	$50.279	$50.28	$50.30	$50.30
Purchase #7	$20.55	11.197%	$22.851	$22.85	$22.85	$22.90
7 purchase totals =	$571.41		$634.2196	$634.22	$634.20	$634.20