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	$240.48	13.333%	$272.5432	$272.54	$272.55	$272.50
Purchase #2	$16.71	11.695%	$18.6642	$18.66	$18.65	$18.70
Purchase #3	$193.50	11.390%	$215.5397	$215.54	$215.55	$215.50
Purchase #4	$119.59	9.830%	$131.3457	$131.35	$131.35	$131.30
Purchase #5	$164.66	3.684%	$170.7261	$170.73	$170.75	$170.70
Purchase #6	$148.66	5.240%	$156.4498	$156.45	$156.45	$156.40
Purchase #7	$50.83	10.811%	$56.3252	$56.33	$56.35	$56.30
7 purchase totals =	$934.43		$1,021.5939	$1,021.60	$1,021.65	$1,021.40