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 $54.91   6.807%   $58.6477   $58.65   $58.65   $58.60  
  Purchase #2 $188.47   11.733%   $210.5832   $210.58   $210.60   $210.60  
  Purchase #3 $89.88   8.633%   $97.6393   $97.64   $97.65   $97.60  
  Purchase #4 $108.41   6.102%   $115.0252   $115.03   $115.05   $115.00  
  Purchase #5 $174.81   6.330%   $185.8755   $185.88   $185.90   $185.90  
  Purchase #6 $221.89   5.406%   $233.8854   $233.89   $233.90   $233.90  
  Purchase #7 $59.59   8.206%   $64.48   $64.48   $64.50   $64.50  
  7 purchase totals = $897.96       $966.1363   $966.15   $966.25   $966.10