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	$59.97	5.851%	$63.4788	$63.48	$63.50	$63.50
Purchase #2	$113.59	6.380%	$120.837	$120.84	$120.85	$120.80
Purchase #3	$77.94	12.641%	$87.7924	$87.79	$87.80	$87.80
Purchase #4	$186.55	12.489%	$209.8482	$209.85	$209.85	$209.80
Purchase #5	$179.47	9.458%	$196.4443	$196.44	$196.45	$196.40
Purchase #6	$39.93	5.262%	$42.0311	$42.03	$42.05	$42.00
Purchase #7	$82.80	3.296%	$85.5291	$85.53	$85.55	$85.50
7 purchase totals =	$740.25		$805.9609	$805.96	$806.05	$805.80