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	$136.56	3.851%	$141.8189	$141.82	$141.80	$141.80
Purchase #2	$133.60	9.697%	$146.5552	$146.56	$146.55	$146.60
Purchase #3	$199.34	5.222%	$209.7495	$209.75	$209.75	$209.70
Purchase #4	$170.77	7.473%	$183.5316	$183.53	$183.55	$183.50
Purchase #5	$42.35	8.346%	$45.8845	$45.88	$45.90	$45.90
Purchase #6	$109.87	5.766%	$116.2051	$116.21	$116.20	$116.20
Purchase #7	$31.53	10.641%	$34.8851	$34.89	$34.90	$34.90
7 purchase totals =	$824.02		$878.6299	$878.64	$878.65	$878.60