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	$43.45	12.604%	$48.9264	$48.93	$48.95	$48.90
Purchase #2	$71.53	6.799%	$76.3933	$76.39	$76.40	$76.40
Purchase #3	$242.47	6.177%	$257.4474	$257.45	$257.45	$257.40
Purchase #4	$37.56	12.394%	$42.2152	$42.22	$42.20	$42.20
Purchase #5	$41.56	3.509%	$43.0183	$43.02	$43.00	$43.00
Purchase #6	$41.61	9.331%	$45.4926	$45.49	$45.50	$45.50
Purchase #7	$197.90	5.847%	$209.4712	$209.47	$209.45	$209.50
7 purchase totals =	$676.08		$722.9644	$722.97	$722.95	$722.90