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	$16.32	11.732%	$18.2347	$18.23	$18.25	$18.20
Purchase #2	$192.29	4.185%	$200.3373	$200.34	$200.35	$200.30
Purchase #3	$80.60	12.777%	$90.8983	$90.90	$90.90	$90.90
Purchase #4	$75.61	8.176%	$81.7919	$81.79	$81.80	$81.80
Purchase #5	$215.55	4.572%	$225.4049	$225.40	$225.40	$225.40
Purchase #6	$172.78	11.380%	$192.4424	$192.44	$192.45	$192.40
Purchase #7	$131.84	9.348%	$144.1644	$144.16	$144.15	$144.20
7 purchase totals =	$884.99		$953.2739	$953.26	$953.30	$953.20