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	$8.46	7.316%	$9.0789	$9.08	$9.10	$9.10
Purchase #2	$136.33	11.410%	$151.8853	$151.89	$151.90	$151.90
Purchase #3	$24.49	5.330%	$25.7953	$25.80	$25.80	$25.80
Purchase #4	$124.48	13.146%	$140.8441	$140.84	$140.85	$140.80
Purchase #5	$60.60	8.429%	$65.708	$65.71	$65.70	$65.70
Purchase #6	$101.38	9.594%	$111.1064	$111.11	$111.10	$111.10
Purchase #7	$177.64	10.544%	$196.3704	$196.37	$196.35	$196.40
7 purchase totals =	$633.38		$700.7884	$700.80	$700.80	$700.80