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	$131.95	8.687%	$143.4125	$143.41	$143.40	$143.40
Purchase #2	$69.31	3.650%	$71.8398	$71.84	$71.85	$71.80
Purchase #3	$84.79	13.656%	$96.3689	$96.37	$96.35	$96.40
Purchase #4	$36.89	9.472%	$40.3842	$40.38	$40.40	$40.40
Purchase #5	$75.31	13.264%	$85.2991	$85.30	$85.30	$85.30
Purchase #6	$217.99	7.325%	$233.9578	$233.96	$233.95	$234.00
Purchase #7	$206.33	10.797%	$228.6075	$228.61	$228.60	$228.60
7 purchase totals =	$822.57		$899.8698	$899.87	$899.85	$899.90