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	$79.79	8.298%	$86.411	$86.41	$86.40	$86.40
Purchase #2	$37.89	5.587%	$40.0069	$40.01	$40.00	$40.00
Purchase #3	$242.26	11.548%	$270.2362	$270.24	$270.25	$270.20
Purchase #4	$197.39	10.323%	$217.7666	$217.77	$217.75	$217.80
Purchase #5	$80.50	4.249%	$83.9204	$83.92	$83.90	$83.90
Purchase #6	$18.82	12.424%	$21.1582	$21.16	$21.15	$21.20
Purchase #7	$63.58	3.729%	$65.9509	$65.95	$65.95	$66.00
7 purchase totals =	$720.23		$785.4502	$785.46	$785.40	$785.50