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	$29.55	6.347%	$31.4255	$31.43	$31.45	$31.40
Purchase #2	$56.48	8.440%	$61.2469	$61.25	$61.25	$61.20
Purchase #3	$189.98	9.534%	$208.0927	$208.09	$208.10	$208.10
Purchase #4	$216.80	12.483%	$243.8631	$243.86	$243.85	$243.90
Purchase #5	$152.95	4.365%	$159.6263	$159.63	$159.65	$159.60
Purchase #6	$95.49	3.869%	$99.1845	$99.18	$99.20	$99.20
Purchase #7	$53.51	5.183%	$56.2834	$56.28	$56.30	$56.30
7 purchase totals =	$794.76		$859.7224	$859.72	$859.80	$859.70