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	$34.54	5.539%	$36.4532	$36.45	$36.45	$36.50
Purchase #2	$39.34	8.221%	$42.5741	$42.57	$42.55	$42.60
Purchase #3	$54.79	7.734%	$59.0275	$59.03	$59.05	$59.00
Purchase #4	$183.98	13.602%	$209.005	$209.01	$209.00	$209.00
Purchase #5	$41.97	4.464%	$43.8435	$43.84	$43.85	$43.80
Purchase #6	$78.63	10.635%	$86.9923	$86.99	$87.00	$87.00
Purchase #7	$37.90	10.769%	$41.9815	$41.98	$42.00	$42.00
7 purchase totals =	$471.15		$519.8771	$519.87	$519.90	$519.90