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	$217.29	10.213%	$239.4818	$239.48	$239.50	$239.50
Purchase #2	$218.52	6.725%	$233.2155	$233.22	$233.20	$233.20
Purchase #3	$74.66	10.387%	$82.4149	$82.41	$82.40	$82.40
Purchase #4	$80.57	9.691%	$88.378	$88.38	$88.40	$88.40
Purchase #5	$131.69	11.716%	$147.1188	$147.12	$147.10	$147.10
Purchase #6	$77.65	10.319%	$85.6627	$85.66	$85.65	$85.70
Purchase #7	$112.89	9.304%	$123.3933	$123.39	$123.40	$123.40
7 purchase totals =	$913.27		$999.6650	$999.66	$999.65	$999.70