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	$20.85	3.789%	$21.64	$21.64	$21.65	$21.60
Purchase #2	$10.99	12.240%	$12.3352	$12.34	$12.35	$12.30
Purchase #3	$133.82	13.681%	$152.1279	$152.13	$152.15	$152.10
Purchase #4	$38.47	12.298%	$43.201	$43.20	$43.20	$43.20
Purchase #5	$244.78	11.341%	$272.5405	$272.54	$272.55	$272.50
Purchase #6	$23.90	8.368%	$25.9	$25.90	$25.90	$25.90
Purchase #7	$232.72	12.329%	$261.412	$261.41	$261.40	$261.40
7 purchase totals =	$705.53		$789.1566	$789.16	$789.20	$789.00