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	$119.61	10.178%	$131.7839	$131.78	$131.80	$131.80
Purchase #2	$126.31	4.133%	$131.5304	$131.53	$131.55	$131.50
Purchase #3	$74.43	10.168%	$81.998	$82.00	$82.00	$82.00
Purchase #4	$40.28	13.181%	$45.5893	$45.59	$45.60	$45.60
Purchase #5	$5.98	10.489%	$6.6072	$6.61	$6.60	$6.60
Purchase #6	$39.85	12.448%	$44.8105	$44.81	$44.80	$44.80
Purchase #7	$143.71	4.147%	$149.6697	$149.67	$149.65	$149.70
7 purchase totals =	$550.17		$591.9890	$591.99	$592.00	$592.00