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	$74.98	10.577%	$82.9106	$82.91	$82.90	$82.90
Purchase #2	$55.59	7.726%	$59.8849	$59.88	$59.90	$59.90
Purchase #3	$176.84	12.323%	$198.632	$198.63	$198.65	$198.60
Purchase #4	$23.98	6.730%	$25.5939	$25.59	$25.60	$25.60
Purchase #5	$215.53	4.806%	$225.8884	$225.89	$225.90	$225.90
Purchase #6	$193.79	4.651%	$202.8032	$202.80	$202.80	$202.80
Purchase #7	$55.54	13.238%	$62.8924	$62.89	$62.90	$62.90
7 purchase totals =	$796.25		$858.6054	$858.59	$858.65	$858.60