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	$31.62	4.391%	$33.0084	$33.01	$33.00	$33.00
Purchase #2	$65.89	9.790%	$72.3406	$72.34	$72.35	$72.30
Purchase #3	$220.39	9.176%	$240.613	$240.61	$240.60	$240.60
Purchase #4	$24.25	7.109%	$25.9739	$25.97	$25.95	$26.00
Purchase #5	$49.85	13.517%	$56.5882	$56.59	$56.60	$56.60
Purchase #6	$58.40	7.347%	$62.6906	$62.69	$62.70	$62.70
Purchase #7	$250.48	13.642%	$284.6505	$284.65	$284.65	$284.70
7 purchase totals =	$700.88		$775.8652	$775.86	$775.85	$775.90