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	$57.50	4.158%	$59.8909	$59.89	$59.90	$59.90
Purchase #2	$81.82	13.224%	$92.6399	$92.64	$92.65	$92.60
Purchase #3	$16.50	9.727%	$18.105	$18.11	$18.10	$18.10
Purchase #4	$196.57	13.648%	$223.3979	$223.40	$223.40	$223.40
Purchase #5	$81.35	6.770%	$86.8574	$86.86	$86.85	$86.90
Purchase #6	$157.85	7.611%	$169.864	$169.86	$169.85	$169.90
Purchase #7	$26.42	11.151%	$29.3661	$29.37	$29.35	$29.40
7 purchase totals =	$618.01		$680.1212	$680.13	$680.10	$680.20