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	$231.89	7.598%	$249.509	$249.51	$249.50	$249.50
Purchase #2	$79.43	12.509%	$89.3659	$89.37	$89.35	$89.40
Purchase #3	$100.98	13.777%	$114.892	$114.89	$114.90	$114.90
Purchase #4	$233.30	4.806%	$244.5124	$244.51	$244.50	$244.50
Purchase #5	$132.54	6.601%	$141.289	$141.29	$141.30	$141.30
Purchase #6	$6.56	8.715%	$7.1317	$7.13	$7.15	$7.10
Purchase #7	$104.97	8.109%	$113.482	$113.48	$113.50	$113.50
7 purchase totals =	$889.67		$960.1820	$960.18	$960.20	$960.20