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	$85.34	4.540%	$89.2144	$89.21	$89.20	$89.20
Purchase #2	$38.77	10.751%	$42.9382	$42.94	$42.95	$42.90
Purchase #3	$182.82	11.714%	$204.2355	$204.24	$204.25	$204.20
Purchase #4	$40.94	8.792%	$44.5394	$44.54	$44.55	$44.50
Purchase #5	$231.61	3.708%	$240.1981	$240.20	$240.20	$240.20
Purchase #6	$40.38	5.704%	$42.6833	$42.68	$42.70	$42.70
Purchase #7	$46.29	12.616%	$52.1299	$52.13	$52.15	$52.10
7 purchase totals =	$666.15		$715.9388	$715.94	$716.00	$715.80