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	$240.31	6.516%	$255.9686	$255.97	$255.95	$256.00
Purchase #2	$32.90	13.204%	$37.2441	$37.24	$37.25	$37.20
Purchase #3	$177.88	5.337%	$187.3735	$187.37	$187.35	$187.40
Purchase #4	$32.37	11.236%	$36.0071	$36.01	$36.00	$36.00
Purchase #5	$226.60	11.147%	$251.8591	$251.86	$251.85	$251.90
Purchase #6	$52.71	13.755%	$59.9603	$59.96	$59.95	$60.00
Purchase #7	$60.86	6.607%	$64.881	$64.88	$64.90	$64.90
7 purchase totals =	$823.63		$893.2937	$893.29	$893.25	$893.40