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	$42.89	4.664%	$44.8904	$44.89	$44.90	$44.90
Purchase #2	$38.98	4.596%	$40.7715	$40.77	$40.75	$40.80
Purchase #3	$178.62	7.481%	$191.9826	$191.98	$192.00	$192.00
Purchase #4	$72.81	6.675%	$77.6701	$77.67	$77.65	$77.70
Purchase #5	$43.86	8.588%	$47.6267	$47.63	$47.65	$47.60
Purchase #6	$120.66	9.151%	$131.7016	$131.70	$131.70	$131.70
Purchase #7	$122.72	12.342%	$137.8661	$137.87	$137.85	$137.90
7 purchase totals =	$620.54		$672.5090	$672.51	$672.50	$672.60