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	$45.94	5.123%	$48.2935	$48.29	$48.30	$48.30
Purchase #2	$172.83	13.749%	$196.5924	$196.59	$196.60	$196.60
Purchase #3	$151.26	4.814%	$158.5417	$158.54	$158.55	$158.50
Purchase #4	$88.49	6.854%	$94.5551	$94.56	$94.55	$94.60
Purchase #5	$170.65	11.868%	$190.9027	$190.90	$190.90	$190.90
Purchase #6	$169.88	8.318%	$184.0106	$184.01	$184.00	$184.00
Purchase #7	$112.81	6.354%	$119.9779	$119.98	$120.00	$120.00
7 purchase totals =	$911.86		$992.8739	$992.87	$992.90	$992.90