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	$135.71	3.438%	$140.3757	$140.38	$140.40	$140.40
Purchase #2	$72.39	7.763%	$78.0096	$78.01	$78.00	$78.00
Purchase #3	$100.43	3.165%	$103.6086	$103.61	$103.60	$103.60
Purchase #4	$231.82	10.436%	$256.0127	$256.01	$256.00	$256.00
Purchase #5	$38.36	6.343%	$40.7932	$40.79	$40.80	$40.80
Purchase #6	$159.40	4.725%	$166.9317	$166.93	$166.95	$166.90
Purchase #7	$20.76	10.845%	$23.0114	$23.01	$23.00	$23.00
7 purchase totals =	$758.87		$808.7429	$808.74	$808.75	$808.70