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	$36.72	10.200%	$40.4654	$40.47	$40.45	$40.50
Purchase #2	$109.93	3.275%	$113.5302	$113.53	$113.55	$113.50
Purchase #3	$227.90	9.384%	$249.2861	$249.29	$249.30	$249.30
Purchase #4	$199.34	12.266%	$223.791	$223.79	$223.80	$223.80
Purchase #5	$86.98	4.601%	$90.9819	$90.98	$91.00	$91.00
Purchase #6	$140.98	8.185%	$152.5192	$152.52	$152.50	$152.50
Purchase #7	$227.35	10.593%	$251.4332	$251.43	$251.45	$251.40
7 purchase totals =	$1,029.20		$1,122.0070	$1,122.01	$1,122.05	$1,122.00