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	$133.51	4.577%	$139.6208	$139.62	$139.60	$139.60
Purchase #2	$5.39	13.734%	$6.1303	$6.13	$6.15	$6.10
Purchase #3	$68.69	9.160%	$74.982	$74.98	$75.00	$75.00
Purchase #4	$77.78	9.848%	$85.4398	$85.44	$85.45	$85.40
Purchase #5	$62.42	8.767%	$67.8924	$67.89	$67.90	$67.90
Purchase #6	$92.84	6.645%	$99.0092	$99.01	$99.00	$99.00
Purchase #7	$31.50	6.334%	$33.4952	$33.50	$33.50	$33.50
7 purchase totals =	$472.13		$506.5697	$506.57	$506.60	$506.50