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	$47.47	13.394%	$53.8281	$53.83	$53.85	$53.80
Purchase #2	$33.55	6.604%	$35.7656	$35.77	$35.75	$35.80
Purchase #3	$124.79	9.477%	$136.6163	$136.62	$136.60	$136.60
Purchase #4	$57.32	4.258%	$59.7607	$59.76	$59.75	$59.80
Purchase #5	$176.49	5.493%	$186.1846	$186.18	$186.20	$186.20
Purchase #6	$40.56	3.534%	$41.9934	$41.99	$42.00	$42.00
Purchase #7	$19.79	8.464%	$21.465	$21.47	$21.45	$21.50
7 purchase totals =	$499.97		$535.6137	$535.62	$535.60	$535.70