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	$41.40	8.429%	$44.8896	$44.89	$44.90	$44.90
Purchase #2	$36.82	13.670%	$41.8533	$41.85	$41.85	$41.90
Purchase #3	$65.70	10.162%	$72.3764	$72.38	$72.40	$72.40
Purchase #4	$74.43	5.519%	$78.5378	$78.54	$78.55	$78.50
Purchase #5	$101.81	8.567%	$110.5321	$110.53	$110.55	$110.50
Purchase #6	$100.34	4.614%	$104.9697	$104.97	$104.95	$105.00
Purchase #7	$76.61	12.519%	$86.2008	$86.20	$86.20	$86.20
7 purchase totals =	$497.11		$539.3597	$539.36	$539.40	$539.40