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	$77.87	13.333%	$88.2524	$88.25	$88.25	$88.30
Purchase #2	$123.62	7.164%	$132.4761	$132.48	$132.50	$132.50
Purchase #3	$201.26	10.448%	$222.2876	$222.29	$222.30	$222.30
Purchase #4	$69.27	3.492%	$71.6889	$71.69	$71.70	$71.70
Purchase #5	$65.32	12.440%	$73.4458	$73.45	$73.45	$73.40
Purchase #6	$111.58	7.437%	$119.8782	$119.88	$119.90	$119.90
Purchase #7	$95.66	6.452%	$101.832	$101.83	$101.85	$101.80
7 purchase totals =	$744.58		$809.8610	$809.87	$809.95	$809.90