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	$187.53	12.127%	$210.2718	$210.27	$210.25	$210.30
Purchase #2	$152.62	4.168%	$158.9812	$158.98	$159.00	$159.00
Purchase #3	$176.30	8.308%	$190.947	$190.95	$190.95	$190.90
Purchase #4	$40.82	11.583%	$45.5482	$45.55	$45.55	$45.50
Purchase #5	$47.43	7.192%	$50.8412	$50.84	$50.85	$50.80
Purchase #6	$72.32	10.636%	$80.012	$80.01	$80.00	$80.00
Purchase #7	$10.37	4.732%	$10.8607	$10.86	$10.85	$10.90
7 purchase totals =	$687.39		$747.4621	$747.46	$747.45	$747.40