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	$37.90	7.730%	$40.8297	$40.83	$40.85	$40.80
Purchase #2	$39.72	4.256%	$41.4105	$41.41	$41.40	$41.40
Purchase #3	$59.35	6.713%	$63.3342	$63.33	$63.35	$63.30
Purchase #4	$87.61	8.486%	$95.0446	$95.04	$95.05	$95.00
Purchase #5	$148.36	8.417%	$160.8475	$160.85	$160.85	$160.80
Purchase #6	$229.35	7.461%	$246.4618	$246.46	$246.45	$246.50
Purchase #7	$35.86	4.634%	$37.5218	$37.52	$37.50	$37.50
7 purchase totals =	$638.15		$685.4501	$685.44	$685.45	$685.30