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	$62.31	8.304%	$67.4842	$67.48	$67.50	$67.50
Purchase #2	$227.59	13.588%	$258.5149	$258.51	$258.50	$258.50
Purchase #3	$249.95	9.134%	$272.7804	$272.78	$272.80	$272.80
Purchase #4	$78.65	8.577%	$85.3958	$85.40	$85.40	$85.40
Purchase #5	$208.47	10.678%	$230.7304	$230.73	$230.75	$230.70
Purchase #6	$36.46	12.557%	$41.0383	$41.04	$41.05	$41.00
Purchase #7	$237.25	11.509%	$264.5551	$264.56	$264.55	$264.60
7 purchase totals =	$1,100.68		$1,220.4991	$1,220.50	$1,220.55	$1,220.50