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	$12.51	7.315%	$13.4251	$13.43	$13.45	$13.40
Purchase #2	$166.31	3.340%	$171.8648	$171.86	$171.85	$171.90
Purchase #3	$43.43	3.538%	$44.9666	$44.97	$44.95	$45.00
Purchase #4	$113.51	8.452%	$123.1039	$123.10	$123.10	$123.10
Purchase #5	$102.87	3.819%	$106.7986	$106.80	$106.80	$106.80
Purchase #6	$144.69	8.136%	$156.462	$156.46	$156.45	$156.50
Purchase #7	$67.78	13.402%	$76.8639	$76.86	$76.85	$76.90
7 purchase totals =	$651.10		$693.4849	$693.48	$693.45	$693.60