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	$41.47	3.275%	$42.8281	$42.83	$42.85	$42.80
Purchase #2	$105.79	13.680%	$120.2621	$120.26	$120.25	$120.30
Purchase #3	$122.39	12.333%	$137.4844	$137.48	$137.50	$137.50
Purchase #4	$14.61	3.804%	$15.1658	$15.17	$15.15	$15.20
Purchase #5	$146.91	6.741%	$156.8132	$156.81	$156.80	$156.80
Purchase #6	$103.56	5.539%	$109.2962	$109.30	$109.30	$109.30
Purchase #7	$203.70	12.784%	$229.741	$229.74	$229.75	$229.70
7 purchase totals =	$738.43		$811.5908	$811.59	$811.60	$811.60