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	$130.99	5.229%	$137.8395	$137.84	$137.85	$137.80
Purchase #2	$204.92	5.562%	$216.3177	$216.32	$216.30	$216.30
Purchase #3	$238.62	6.354%	$253.7819	$253.78	$253.80	$253.80
Purchase #4	$38.55	10.440%	$42.5746	$42.57	$42.55	$42.60
Purchase #5	$76.97	7.218%	$82.5257	$82.53	$82.55	$82.50
Purchase #6	$95.26	5.790%	$100.7756	$100.78	$100.80	$100.80
Purchase #7	$113.70	3.512%	$117.6931	$117.69	$117.70	$117.70
7 purchase totals =	$899.01		$951.5081	$951.51	$951.55	$951.50