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	$11.55	12.424%	$12.985	$12.99	$13.00	$13.00
Purchase #2	$84.79	6.156%	$90.0097	$90.01	$90.00	$90.00
Purchase #3	$124.89	5.368%	$131.5941	$131.59	$131.60	$131.60
Purchase #4	$180.62	5.428%	$190.4241	$190.42	$190.40	$190.40
Purchase #5	$162.89	7.837%	$175.6557	$175.66	$175.65	$175.70
Purchase #6	$191.55	4.393%	$199.9648	$199.96	$199.95	$200.00
Purchase #7	$143.61	12.709%	$161.8614	$161.86	$161.85	$161.90
7 purchase totals =	$899.90		$962.4948	$962.49	$962.45	$962.60