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	$104.94	7.862%	$113.1904	$113.19	$113.20	$113.20
Purchase #2	$109.31	9.301%	$119.4769	$119.48	$119.50	$119.50
Purchase #3	$196.97	7.129%	$211.012	$211.01	$211.00	$211.00
Purchase #4	$102.32	6.151%	$108.6137	$108.61	$108.60	$108.60
Purchase #5	$222.61	8.309%	$241.1067	$241.11	$241.10	$241.10
Purchase #6	$72.97	12.628%	$82.1847	$82.18	$82.20	$82.20
Purchase #7	$111.95	5.307%	$117.8912	$117.89	$117.90	$117.90
7 purchase totals =	$921.07		$993.4756	$993.47	$993.50	$993.50