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	$27.42	6.731%	$29.2656	$29.27	$29.25	$29.30
Purchase #2	$98.85	10.606%	$109.334	$109.33	$109.35	$109.30
Purchase #3	$161.33	12.840%	$182.0448	$182.04	$182.05	$182.00
Purchase #4	$68.80	4.759%	$72.0742	$72.07	$72.05	$72.10
Purchase #5	$250.45	6.102%	$265.7325	$265.73	$265.75	$265.70
Purchase #6	$23.54	5.738%	$24.8907	$24.89	$24.90	$24.90
Purchase #7	$51.93	13.342%	$58.8585	$58.86	$58.85	$58.90
7 purchase totals =	$682.32		$742.2003	$742.19	$742.20	$742.20