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	$215.50	13.660%	$244.9373	$244.94	$244.95	$244.90
Purchase #2	$39.29	8.124%	$42.4819	$42.48	$42.50	$42.50
Purchase #3	$88.92	7.458%	$95.5517	$95.55	$95.55	$95.60
Purchase #4	$44.51	6.785%	$47.53	$47.53	$47.55	$47.50
Purchase #5	$39.98	11.585%	$44.6117	$44.61	$44.60	$44.60
Purchase #6	$88.33	12.789%	$99.6265	$99.63	$99.65	$99.60
Purchase #7	$62.56	8.413%	$67.8232	$67.82	$67.80	$67.80
7 purchase totals =	$579.09		$642.5623	$642.56	$642.60	$642.50