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	$52.87	8.761%	$57.5019	$57.50	$57.50	$57.50
Purchase #2	$139.77	7.542%	$150.3115	$150.31	$150.30	$150.30
Purchase #3	$87.76	12.627%	$98.8415	$98.84	$98.85	$98.80
Purchase #4	$92.81	10.556%	$102.607	$102.61	$102.60	$102.60
Purchase #5	$190.55	6.455%	$202.85	$202.85	$202.85	$202.90
Purchase #6	$52.25	13.308%	$59.2034	$59.20	$59.20	$59.20
Purchase #7	$215.48	3.217%	$222.412	$222.41	$222.40	$222.40
7 purchase totals =	$831.49		$893.7273	$893.72	$893.70	$893.70