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	$150.40	13.541%	$170.7657	$170.77	$170.75	$170.80
Purchase #2	$19.68	11.311%	$21.906	$21.91	$21.90	$21.90
Purchase #3	$214.72	5.764%	$227.0965	$227.10	$227.10	$227.10
Purchase #4	$73.29	12.409%	$82.3846	$82.38	$82.40	$82.40
Purchase #5	$135.27	3.834%	$140.4563	$140.46	$140.45	$140.50
Purchase #6	$44.83	9.222%	$48.9642	$48.96	$48.95	$49.00
Purchase #7	$33.91	11.748%	$37.8937	$37.89	$37.90	$37.90
7 purchase totals =	$672.10		$729.4670	$729.47	$729.45	$729.60