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	$236.72	5.666%	$250.1326	$250.13	$250.15	$250.10
Purchase #2	$146.38	9.648%	$160.5027	$160.50	$160.50	$160.50
Purchase #3	$219.81	7.365%	$235.999	$236.00	$236.00	$236.00
Purchase #4	$130.87	11.870%	$146.4043	$146.40	$146.40	$146.40
Purchase #5	$247.69	10.401%	$273.4522	$273.45	$273.45	$273.50
Purchase #6	$122.88	13.774%	$139.8055	$139.81	$139.80	$139.80
Purchase #7	$185.88	7.586%	$199.9809	$199.98	$200.00	$200.00
7 purchase totals =	$1,290.23		$1,406.2772	$1,406.27	$1,406.30	$1,406.30