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	$129.94	5.702%	$137.3492	$137.35	$137.35	$137.30
Purchase #2	$166.70	7.601%	$179.3709	$179.37	$179.35	$179.40
Purchase #3	$242.32	4.481%	$253.1784	$253.18	$253.20	$253.20
Purchase #4	$55.34	8.554%	$60.0738	$60.07	$60.05	$60.10
Purchase #5	$80.28	6.592%	$85.5721	$85.57	$85.55	$85.60
Purchase #6	$164.61	10.279%	$181.5303	$181.53	$181.55	$181.50
Purchase #7	$37.94	7.620%	$40.831	$40.83	$40.85	$40.80
7 purchase totals =	$877.13		$937.9057	$937.90	$937.90	$937.90