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	$131.52	3.635%	$136.3008	$136.30	$136.30	$136.30
Purchase #2	$172.95	7.441%	$185.8192	$185.82	$185.80	$185.80
Purchase #3	$39.87	7.563%	$42.8854	$42.89	$42.90	$42.90
Purchase #4	$15.57	11.306%	$17.3303	$17.33	$17.35	$17.30
Purchase #5	$167.82	13.599%	$190.6418	$190.64	$190.65	$190.60
Purchase #6	$227.82	5.489%	$240.325	$240.33	$240.35	$240.30
Purchase #7	$9.75	10.536%	$10.7773	$10.78	$10.80	$10.80
7 purchase totals =	$765.30		$824.0798	$824.09	$824.15	$824.00