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	$33.73	12.264%	$37.8666	$37.87	$37.85	$37.90
Purchase #2	$29.29	12.248%	$32.8774	$32.88	$32.90	$32.90
Purchase #3	$120.36	13.704%	$136.8541	$136.85	$136.85	$136.90
Purchase #4	$214.66	12.795%	$242.1257	$242.13	$242.15	$242.10
Purchase #5	$139.51	5.712%	$147.4788	$147.48	$147.50	$147.50
Purchase #6	$19.77	10.858%	$21.9166	$21.92	$21.90	$21.90
Purchase #7	$45.51	4.785%	$47.6877	$47.69	$47.70	$47.70
7 purchase totals =	$602.83		$666.8069	$666.82	$666.85	$666.90