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	$236.43	6.504%	$251.8074	$251.81	$251.80	$251.80
Purchase #2	$216.48	6.237%	$229.9819	$229.98	$230.00	$230.00
Purchase #3	$107.48	6.556%	$114.5264	$114.53	$114.55	$114.50
Purchase #4	$37.39	7.216%	$40.0881	$40.09	$40.10	$40.10
Purchase #5	$114.54	12.458%	$128.8094	$128.81	$128.80	$128.80
Purchase #6	$55.55	3.494%	$57.4909	$57.49	$57.50	$57.50
Purchase #7	$145.29	7.302%	$155.8991	$155.90	$155.90	$155.90
7 purchase totals =	$913.16		$978.6032	$978.61	$978.65	$978.60