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 $112.35   12.772%   $126.6993   $126.70   $126.70   $126.70  
  Purchase #2 $176.63   3.524%   $182.8544   $182.85   $182.85   $182.90  
  Purchase #3 $246.43   6.154%   $261.5953   $261.60   $261.60   $261.60  
  Purchase #4 $6.33   6.171%   $6.7206   $6.72   $6.70   $6.70  
  Purchase #5 $68.83   9.772%   $75.5561   $75.56   $75.55   $75.60  
  Purchase #6 $237.63   13.828%   $270.4895   $270.49   $270.50   $270.50  
  Purchase #7 $18.48   6.791%   $19.735   $19.74   $19.75   $19.70  
  7 purchase totals = $866.68       $943.6502   $943.66   $943.65   $943.70