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 $58.34   13.199%   $66.0403   $66.04   $66.05   $66.00  
  Purchase #2 $60.98   7.565%   $65.5931   $65.59   $65.60   $65.60  
  Purchase #3 $73.74   13.819%   $83.9301   $83.93   $83.95   $83.90  
  Purchase #4 $249.79   6.573%   $266.2087   $266.21   $266.20   $266.20  
  Purchase #5 $151.37   4.857%   $158.722   $158.72   $158.70   $158.70  
  Purchase #6 $210.57   8.102%   $227.6304   $227.63   $227.65   $227.60  
  Purchase #7 $237.92   8.155%   $257.3224   $257.32   $257.30   $257.30  
  7 purchase totals = $1,042.71       $1,125.4470   $1,125.44   $1,125.45   $1,125.30