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 $30.62   11.408%   $34.1131   $34.11   $34.10   $34.10  
  Purchase #2 $245.58   5.706%   $259.5928   $259.59   $259.60   $259.60  
  Purchase #3 $70.56   12.731%   $79.543   $79.54   $79.55   $79.50  
  Purchase #4 $195.54   7.563%   $210.3287   $210.33   $210.35   $210.30  
  Purchase #5 $70.50   11.727%   $78.7675   $78.77   $78.75   $78.80  
  Purchase #6 $154.98   5.699%   $163.8123   $163.81   $163.80   $163.80  
  Purchase #7 $204.78   6.850%   $218.8074   $218.81   $218.80   $218.80  
  7 purchase totals = $972.56       $1,044.9648   $1,044.96   $1,044.95   $1,044.90