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	$57.76	12.347%	$64.8916	$64.89	$64.90	$64.90
Purchase #2	$25.92	13.843%	$29.5081	$29.51	$29.50	$29.50
Purchase #3	$179.74	4.352%	$187.5623	$187.56	$187.55	$187.60
Purchase #4	$164.57	3.188%	$169.8165	$169.82	$169.80	$169.80
Purchase #5	$215.37	11.695%	$240.5575	$240.56	$240.55	$240.60
Purchase #6	$50.72	12.554%	$57.0874	$57.09	$57.10	$57.10
Purchase #7	$169.27	12.754%	$190.8587	$190.86	$190.85	$190.90
7 purchase totals =	$863.35		$940.2821	$940.29	$940.25	$940.40