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 $59.36   10.726%   $65.727   $65.73   $65.75   $65.70  
  Purchase #2 $211.46   11.219%   $235.1837   $235.18   $235.20   $235.20  
  Purchase #3 $176.78   8.154%   $191.1946   $191.19   $191.20   $191.20  
  Purchase #4 $15.49   12.269%   $17.3905   $17.39   $17.40   $17.40  
  Purchase #5 $195.68   6.582%   $208.5597   $208.56   $208.55   $208.60  
  Purchase #6 $96.46   13.110%   $109.1059   $109.11   $109.10   $109.10  
  Purchase #7 $161.92   5.489%   $170.8078   $170.81   $170.80   $170.80  
  7 purchase totals = $917.15       $997.9692   $997.97   $998.00   $998.00