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	$45.78	13.350%	$51.8916	$51.89	$51.90	$51.90
Purchase #2	$116.79	12.551%	$131.4483	$131.45	$131.45	$131.40
Purchase #3	$52.93	4.732%	$55.4346	$55.43	$55.45	$55.40
Purchase #4	$248.95	8.637%	$270.4518	$270.45	$270.45	$270.50
Purchase #5	$23.56	9.655%	$25.8347	$25.83	$25.85	$25.80
Purchase #6	$212.95	6.274%	$226.3105	$226.31	$226.30	$226.30
Purchase #7	$144.43	7.680%	$155.5222	$155.52	$155.50	$155.50
7 purchase totals =	$845.39		$916.8937	$916.88	$916.90	$916.80