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	$132.66	7.164%	$142.1638	$142.16	$142.15	$142.20
Purchase #2	$162.82	8.519%	$176.6906	$176.69	$176.70	$176.70
Purchase #3	$207.95	11.149%	$231.1343	$231.13	$231.15	$231.10
Purchase #4	$174.94	11.184%	$194.5053	$194.51	$194.50	$194.50
Purchase #5	$91.46	9.387%	$100.0454	$100.05	$100.05	$100.00
Purchase #6	$169.98	12.114%	$190.5714	$190.57	$190.55	$190.60
Purchase #7	$249.28	9.472%	$272.8918	$272.89	$272.90	$272.90
7 purchase totals =	$1,189.09		$1,308.0026	$1,308.00	$1,308.00	$1,308.00