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	$78.88	4.339%	$82.3026	$82.30	$82.30	$82.30
Purchase #2	$213.86	5.623%	$225.8853	$225.89	$225.90	$225.90
Purchase #3	$21.47	13.439%	$24.3554	$24.36	$24.35	$24.40
Purchase #4	$36.82	7.519%	$39.5885	$39.59	$39.60	$39.60
Purchase #5	$150.82	11.378%	$167.9803	$167.98	$168.00	$168.00
Purchase #6	$127.47	12.561%	$143.4815	$143.48	$143.50	$143.50
Purchase #7	$239.75	8.287%	$259.6181	$259.62	$259.60	$259.60
7 purchase totals =	$869.07		$943.2117	$943.22	$943.25	$943.30