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	$54.58	9.762%	$59.9081	$59.91	$59.90	$59.90
Purchase #2	$30.45	8.304%	$32.9786	$32.98	$33.00	$33.00
Purchase #3	$236.72	10.473%	$261.5117	$261.51	$261.50	$261.50
Purchase #4	$235.37	5.746%	$248.8944	$248.89	$248.90	$248.90
Purchase #5	$102.34	10.257%	$112.837	$112.84	$112.85	$112.80
Purchase #6	$64.93	6.295%	$69.0173	$69.02	$69.00	$69.00
Purchase #7	$24.83	10.158%	$27.3522	$27.35	$27.35	$27.40
7 purchase totals =	$749.22		$812.4993	$812.50	$812.50	$812.50