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	$53.90	3.656%	$55.8706	$55.87	$55.85	$55.90
Purchase #2	$46.87	6.316%	$49.8303	$49.83	$49.85	$49.80
Purchase #3	$171.27	3.568%	$177.3809	$177.38	$177.40	$177.40
Purchase #4	$164.50	4.257%	$171.5028	$171.50	$171.50	$171.50
Purchase #5	$82.82	7.204%	$88.7864	$88.79	$88.80	$88.80
Purchase #6	$41.47	4.502%	$43.337	$43.34	$43.35	$43.30
Purchase #7	$90.62	12.442%	$101.8949	$101.89	$101.90	$101.90
7 purchase totals =	$651.45		$688.6029	$688.60	$688.65	$688.60