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	$29.89	5.690%	$31.5907	$31.59	$31.60	$31.60
Purchase #2	$40.81	4.140%	$42.4995	$42.50	$42.50	$42.50
Purchase #3	$36.65	7.287%	$39.3207	$39.32	$39.30	$39.30
Purchase #4	$90.66	10.408%	$100.0959	$100.10	$100.10	$100.10
Purchase #5	$221.25	4.576%	$231.3744	$231.37	$231.35	$231.40
Purchase #6	$215.70	10.759%	$238.9072	$238.91	$238.90	$238.90
Purchase #7	$213.49	5.191%	$224.5723	$224.57	$224.55	$224.60
7 purchase totals =	$848.45		$908.3607	$908.36	$908.30	$908.40