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	$237.37	5.274%	$249.8889	$249.89	$249.90	$249.90
Purchase #2	$178.53	10.108%	$196.5758	$196.58	$196.60	$196.60
Purchase #3	$156.98	3.204%	$162.0096	$162.01	$162.00	$162.00
Purchase #4	$73.27	13.745%	$83.341	$83.34	$83.35	$83.30
Purchase #5	$19.36	6.565%	$20.631	$20.63	$20.65	$20.60
Purchase #6	$38.50	9.802%	$42.2738	$42.27	$42.25	$42.30
Purchase #7	$44.89	10.717%	$49.7009	$49.70	$49.70	$49.70
7 purchase totals =	$748.90		$804.4210	$804.42	$804.45	$804.40