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	$117.82	8.127%	$127.3952	$127.40	$127.40	$127.40
Purchase #2	$58.66	6.363%	$62.3925	$62.39	$62.40	$62.40
Purchase #3	$123.98	7.283%	$133.0095	$133.01	$133.00	$133.00
Purchase #4	$178.26	10.157%	$196.3659	$196.37	$196.35	$196.40
Purchase #5	$41.31	6.187%	$43.8658	$43.87	$43.85	$43.90
Purchase #6	$66.49	10.849%	$73.7035	$73.70	$73.70	$73.70
Purchase #7	$237.48	7.228%	$254.6451	$254.65	$254.65	$254.60
7 purchase totals =	$824.00		$891.3775	$891.39	$891.35	$891.40