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	$30.53	7.479%	$32.8133	$32.81	$32.80	$32.80
Purchase #2	$111.96	10.630%	$123.8613	$123.86	$123.85	$123.90
Purchase #3	$14.44	6.231%	$15.3398	$15.34	$15.35	$15.30
Purchase #4	$9.90	8.871%	$10.7782	$10.78	$10.80	$10.80
Purchase #5	$233.79	13.582%	$265.5434	$265.54	$265.55	$265.50
Purchase #6	$77.74	11.154%	$86.4111	$86.41	$86.40	$86.40
Purchase #7	$87.70	7.716%	$94.4669	$94.47	$94.45	$94.50
7 purchase totals =	$566.06		$629.2140	$629.21	$629.20	$629.20