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	$57.49	4.160%	$59.8816	$59.88	$59.90	$59.90
Purchase #2	$112.68	5.421%	$118.7884	$118.79	$118.80	$118.80
Purchase #3	$8.79	8.408%	$9.5291	$9.53	$9.55	$9.50
Purchase #4	$240.40	7.266%	$257.8675	$257.87	$257.85	$257.90
Purchase #5	$75.70	4.121%	$78.8196	$78.82	$78.80	$78.80
Purchase #6	$132.89	11.831%	$148.6122	$148.61	$148.60	$148.60
Purchase #7	$136.89	5.848%	$144.8953	$144.90	$144.90	$144.90
7 purchase totals =	$764.84		$818.3937	$818.40	$818.40	$818.40