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 $61.97   4.416%   $64.7066   $64.71   $64.70   $64.70  
  Purchase #2 $234.80   3.425%   $242.8419   $242.84   $242.85   $242.80  
  Purchase #3 $66.44   4.521%   $69.4438   $69.44   $69.45   $69.40  
  Purchase #4 $30.73   3.509%   $31.8083   $31.81   $31.80   $31.80  
  Purchase #5 $58.73   3.174%   $60.5941   $60.59   $60.60   $60.60  
  Purchase #6 $134.90   6.264%   $143.3501   $143.35   $143.35   $143.40  
  Purchase #7 $122.62   4.184%   $127.7504   $127.75   $127.75   $127.80  
  7 purchase totals = $710.19       $740.4952   $740.49   $740.50   $740.50