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	$37.94	9.645%	$41.5993	$41.60	$41.60	$41.60
Purchase #2	$31.78	13.120%	$35.9495	$35.95	$35.95	$35.90
Purchase #3	$170.81	11.546%	$190.5317	$190.53	$190.55	$190.50
Purchase #4	$101.68	4.164%	$105.914	$105.91	$105.90	$105.90
Purchase #5	$27.28	12.526%	$30.6971	$30.70	$30.70	$30.70
Purchase #6	$43.53	12.324%	$48.8946	$48.89	$48.90	$48.90
Purchase #7	$117.74	11.390%	$131.1506	$131.15	$131.15	$131.20
7 purchase totals =	$530.76		$584.7368	$584.73	$584.75	$584.70