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	$125.83	10.332%	$138.8308	$138.83	$138.85	$138.80
Purchase #2	$249.57	4.793%	$261.5319	$261.53	$261.55	$261.50
Purchase #3	$29.87	12.484%	$33.599	$33.60	$33.60	$33.60
Purchase #4	$88.53	12.193%	$99.3245	$99.32	$99.30	$99.30
Purchase #5	$109.48	13.444%	$124.1985	$124.20	$124.20	$124.20
Purchase #6	$64.63	11.321%	$71.9468	$71.95	$71.95	$71.90
Purchase #7	$219.59	8.577%	$238.4242	$238.42	$238.40	$238.40
7 purchase totals =	$887.50		$967.8557	$967.85	$967.85	$967.70