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	$139.77	12.189%	$156.8066	$156.81	$156.80	$156.80
Purchase #2	$131.33	12.353%	$147.5532	$147.55	$147.55	$147.60
Purchase #3	$143.98	3.342%	$148.7918	$148.79	$148.80	$148.80
Purchase #4	$199.38	13.796%	$226.8865	$226.89	$226.90	$226.90
Purchase #5	$27.47	8.565%	$29.8228	$29.82	$29.80	$29.80
Purchase #6	$44.59	13.142%	$50.45	$50.45	$50.45	$50.50
Purchase #7	$223.50	9.772%	$245.3404	$245.34	$245.35	$245.30
7 purchase totals =	$910.02		$1,005.6513	$1,005.65	$1,005.65	$1,005.70