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	$132.59	6.643%	$141.398	$141.40	$141.40	$141.40
Purchase #2	$232.93	4.493%	$243.3955	$243.40	$243.40	$243.40
Purchase #3	$121.92	7.278%	$130.7933	$130.79	$130.80	$130.80
Purchase #4	$52.77	12.706%	$59.475	$59.48	$59.50	$59.50
Purchase #5	$182.89	13.606%	$207.774	$207.77	$207.75	$207.80
Purchase #6	$6.31	13.865%	$7.1849	$7.18	$7.20	$7.20
Purchase #7	$54.66	8.752%	$59.4438	$59.44	$59.45	$59.40
7 purchase totals =	$784.07		$849.4645	$849.46	$849.50	$849.50