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	$43.37	13.554%	$49.2484	$49.25	$49.25	$49.20
Purchase #2	$25.28	8.399%	$27.4033	$27.40	$27.40	$27.40
Purchase #3	$16.59	10.136%	$18.2716	$18.27	$18.25	$18.30
Purchase #4	$18.54	9.472%	$20.2961	$20.30	$20.30	$20.30
Purchase #5	$150.59	3.770%	$156.2672	$156.27	$156.25	$156.30
Purchase #6	$213.82	6.292%	$227.2736	$227.27	$227.25	$227.30
Purchase #7	$131.56	6.471%	$140.0732	$140.07	$140.05	$140.10
7 purchase totals =	$599.75		$638.8334	$638.83	$638.75	$638.90