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	$7.40	7.863%	$7.9819	$7.98	$8.00	$8.00
Purchase #2	$73.63	6.574%	$78.4704	$78.47	$78.45	$78.50
Purchase #3	$216.97	10.685%	$240.1532	$240.15	$240.15	$240.20
Purchase #4	$189.29	13.490%	$214.8252	$214.83	$214.85	$214.80
Purchase #5	$214.71	3.436%	$222.0874	$222.09	$222.10	$222.10
Purchase #6	$136.73	3.657%	$141.7302	$141.73	$141.75	$141.70
Purchase #7	$196.61	12.472%	$221.1312	$221.13	$221.15	$221.10
7 purchase totals =	$1,035.34		$1,126.3795	$1,126.38	$1,126.45	$1,126.40