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	$150.57	10.860%	$166.9219	$166.92	$166.90	$166.90
Purchase #2	$20.66	11.766%	$23.0909	$23.09	$23.10	$23.10
Purchase #3	$131.56	9.174%	$143.6293	$143.63	$143.65	$143.60
Purchase #4	$248.71	10.357%	$274.4689	$274.47	$274.45	$274.50
Purchase #5	$47.46	11.538%	$52.9359	$52.94	$52.95	$52.90
Purchase #6	$133.47	8.568%	$144.9057	$144.91	$144.90	$144.90
Purchase #7	$63.50	13.315%	$71.955	$71.96	$71.95	$72.00
7 purchase totals =	$795.93		$877.9076	$877.92	$877.90	$877.90