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 $53.87   13.536%   $61.1618   $61.16   $61.15   $61.20  
  Purchase #2 $171.62   11.661%   $191.6326   $191.63   $191.65   $191.60  
  Purchase #3 $193.56   3.156%   $199.6688   $199.67   $199.65   $199.70  
  Purchase #4 $76.87   11.453%   $85.6739   $85.67   $85.65   $85.70  
  Purchase #5 $174.74   10.627%   $193.3096   $193.31   $193.30   $193.30  
  Purchase #6 $53.86   5.204%   $56.6629   $56.66   $56.65   $56.70  
  Purchase #7 $134.31   6.412%   $142.922   $142.92   $142.90   $142.90  
  7 purchase totals = $858.83       $931.0316   $931.02   $930.95   $931.10