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	$202.75	9.789%	$222.5972	$222.60	$222.60	$222.60
Purchase #2	$64.49	3.172%	$66.5356	$66.54	$66.55	$66.50
Purchase #3	$110.90	5.785%	$117.3156	$117.32	$117.30	$117.30
Purchase #4	$32.89	5.245%	$34.6151	$34.62	$34.60	$34.60
Purchase #5	$106.68	9.206%	$116.501	$116.50	$116.50	$116.50
Purchase #6	$93.86	7.145%	$100.5663	$100.57	$100.55	$100.60
Purchase #7	$183.96	8.303%	$199.2342	$199.23	$199.25	$199.20
7 purchase totals =	$795.53		$857.3650	$857.38	$857.35	$857.30