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	$44.27	10.456%	$48.8989	$48.90	$48.90	$48.90
Purchase #2	$31.55	5.850%	$33.3957	$33.40	$33.40	$33.40
Purchase #3	$249.54	4.694%	$261.2534	$261.25	$261.25	$261.30
Purchase #4	$160.47	4.557%	$167.7826	$167.78	$167.80	$167.80
Purchase #5	$241.49	9.434%	$264.2722	$264.27	$264.25	$264.30
Purchase #6	$13.98	13.215%	$15.8275	$15.83	$15.85	$15.80
Purchase #7	$123.36	8.847%	$134.2737	$134.27	$134.25	$134.30
7 purchase totals =	$864.66		$925.7040	$925.70	$925.70	$925.80