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	$185.79	11.103%	$206.4183	$206.42	$206.40	$206.40
Purchase #2	$81.60	6.432%	$86.8485	$86.85	$86.85	$86.80
Purchase #3	$98.64	3.481%	$102.0737	$102.07	$102.05	$102.10
Purchase #4	$37.84	4.561%	$39.5659	$39.57	$39.55	$39.60
Purchase #5	$69.63	10.682%	$77.0679	$77.07	$77.05	$77.10
Purchase #6	$38.42	4.146%	$40.0129	$40.01	$40.00	$40.00
Purchase #7	$77.34	6.659%	$82.4901	$82.49	$82.50	$82.50
7 purchase totals =	$589.26		$634.4773	$634.48	$634.40	$634.50