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	$136.92	9.854%	$150.4121	$150.41	$150.40	$150.40
Purchase #2	$76.95	7.181%	$82.4758	$82.48	$82.50	$82.50
Purchase #3	$215.64	10.509%	$238.3016	$238.30	$238.30	$238.30
Purchase #4	$242.25	13.201%	$274.2294	$274.23	$274.25	$274.20
Purchase #5	$26.41	12.798%	$29.79	$29.79	$29.80	$29.80
Purchase #6	$199.73	4.588%	$208.8936	$208.89	$208.90	$208.90
Purchase #7	$124.32	13.230%	$140.7675	$140.77	$140.75	$140.80
7 purchase totals =	$1,022.22		$1,124.8700	$1,124.87	$1,124.90	$1,124.90