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	$217.70	9.452%	$238.277	$238.28	$238.30	$238.30
Purchase #2	$170.46	8.718%	$185.3207	$185.32	$185.30	$185.30
Purchase #3	$140.88	12.249%	$158.1364	$158.14	$158.15	$158.10
Purchase #4	$75.86	11.558%	$84.6279	$84.63	$84.65	$84.60
Purchase #5	$161.54	11.458%	$180.0493	$180.05	$180.05	$180.00
Purchase #6	$127.89	11.650%	$142.7892	$142.79	$142.80	$142.80
Purchase #7	$137.41	9.282%	$150.1644	$150.16	$150.15	$150.20
7 purchase totals =	$1,031.74		$1,139.3649	$1,139.37	$1,139.40	$1,139.30