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	$39.46	8.646%	$42.8717	$42.87	$42.85	$42.90
Purchase #2	$136.83	7.239%	$146.7351	$146.74	$146.75	$146.70
Purchase #3	$88.74	5.110%	$93.2746	$93.27	$93.25	$93.30
Purchase #4	$153.51	9.203%	$167.6375	$167.64	$167.65	$167.60
Purchase #5	$41.91	4.739%	$43.8961	$43.90	$43.90	$43.90
Purchase #6	$235.59	11.728%	$263.22	$263.22	$263.20	$263.20
Purchase #7	$90.58	11.428%	$100.9315	$100.93	$100.95	$100.90
7 purchase totals =	$786.62		$858.5665	$858.57	$858.55	$858.50