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	$12.26	9.383%	$13.4104	$13.41	$13.40	$13.40
Purchase #2	$42.65	5.315%	$44.9168	$44.92	$44.90	$44.90
Purchase #3	$240.34	13.457%	$272.6826	$272.68	$272.70	$272.70
Purchase #4	$161.54	5.786%	$170.8867	$170.89	$170.90	$170.90
Purchase #5	$33.55	11.207%	$37.3099	$37.31	$37.30	$37.30
Purchase #6	$159.47	7.566%	$171.5355	$171.54	$171.55	$171.50
Purchase #7	$200.41	10.866%	$222.1866	$222.19	$222.20	$222.20
7 purchase totals =	$850.22		$932.9285	$932.94	$932.95	$932.90