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	$18.35	11.731%	$20.5026	$20.50	$20.50	$20.50
Purchase #2	$206.28	4.582%	$215.7317	$215.73	$215.75	$215.70
Purchase #3	$110.56	5.253%	$116.3677	$116.37	$116.35	$116.40
Purchase #4	$10.55	13.821%	$12.0081	$12.01	$12.00	$12.00
Purchase #5	$24.48	7.714%	$26.3684	$26.37	$26.35	$26.40
Purchase #6	$52.34	12.736%	$59.006	$59.01	$59.00	$59.00
Purchase #7	$163.78	3.556%	$169.604	$169.60	$169.60	$169.60
7 purchase totals =	$586.34		$619.5885	$619.59	$619.55	$619.60