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 $244.97   11.719%   $273.678   $273.68   $273.70   $273.70  
  Purchase #2 $51.48   5.146%   $54.1292   $54.13   $54.15   $54.10  
  Purchase #3 $74.73   13.863%   $85.0898   $85.09   $85.10   $85.10  
  Purchase #4 $112.38   4.822%   $117.799   $117.80   $117.80   $117.80  
  Purchase #5 $55.89   4.398%   $58.348   $58.35   $58.35   $58.30  
  Purchase #6 $188.83   5.320%   $198.8758   $198.88   $198.90   $198.90  
  Purchase #7 $224.93   7.794%   $242.461   $242.46   $242.45   $242.50  
  7 purchase totals = $953.21       $1,030.3808   $1,030.39   $1,030.45   $1,030.40