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	$9.89	10.291%	$10.9078	$10.91	$10.90	$10.90
Purchase #2	$97.29	12.853%	$109.7947	$109.79	$109.80	$109.80
Purchase #3	$23.36	8.538%	$25.3545	$25.35	$25.35	$25.40
Purchase #4	$55.39	6.687%	$59.0939	$59.09	$59.10	$59.10
Purchase #5	$112.47	4.696%	$117.7516	$117.75	$117.75	$117.80
Purchase #6	$76.77	11.650%	$85.7137	$85.71	$85.70	$85.70
Purchase #7	$111.78	5.526%	$117.957	$117.96	$117.95	$118.00
7 purchase totals =	$486.95		$526.5732	$526.56	$526.55	$526.70