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	$29.82	12.652%	$33.5928	$33.59	$33.60	$33.60
Purchase #2	$39.34	3.534%	$40.7303	$40.73	$40.75	$40.70
Purchase #3	$36.65	4.687%	$38.3678	$38.37	$38.35	$38.40
Purchase #4	$43.69	11.435%	$48.686	$48.69	$48.70	$48.70
Purchase #5	$243.65	8.669%	$264.772	$264.77	$264.75	$264.80
Purchase #6	$112.70	6.389%	$119.9004	$119.90	$119.90	$119.90
Purchase #7	$124.25	8.145%	$134.3702	$134.37	$134.35	$134.40
7 purchase totals =	$630.10		$680.4195	$680.42	$680.40	$680.50