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	$33.51	5.868%	$35.4764	$35.48	$35.50	$35.50
Purchase #2	$48.64	7.412%	$52.2452	$52.25	$52.25	$52.20
Purchase #3	$50.79	10.103%	$55.9213	$55.92	$55.90	$55.90
Purchase #4	$248.95	7.433%	$267.4545	$267.45	$267.45	$267.50
Purchase #5	$216.55	5.542%	$228.5512	$228.55	$228.55	$228.60
Purchase #6	$190.76	5.110%	$200.5078	$200.51	$200.50	$200.50
Purchase #7	$124.85	12.203%	$140.0854	$140.09	$140.10	$140.10
7 purchase totals =	$914.05		$980.2418	$980.25	$980.25	$980.30