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 $242.49   13.303%   $274.7484   $274.75   $274.75   $274.70  
  Purchase #2 $105.37   13.354%   $119.4411   $119.44   $119.45   $119.40  
  Purchase #3 $151.35   12.796%   $170.7167   $170.72   $170.70   $170.70  
  Purchase #4 $104.94   12.147%   $117.6871   $117.69   $117.70   $117.70  
  Purchase #5 $23.73   9.261%   $25.9276   $25.93   $25.95   $25.90  
  Purchase #6 $162.25   11.498%   $180.9055   $180.91   $180.90   $180.90  
  Purchase #7 $235.84   9.816%   $258.9901   $258.99   $259.00   $259.00  
  7 purchase totals = $1,025.97       $1,148.4165   $1,148.43   $1,148.45   $1,148.30