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 $141.46   13.115%   $160.0125   $160.01   $160.00   $160.00  
  Purchase #2 $87.70   9.849%   $96.3376   $96.34   $96.35   $96.30  
  Purchase #3 $26.92   12.792%   $30.3636   $30.36   $30.35   $30.40  
  Purchase #4 $136.49   11.787%   $152.5781   $152.58   $152.60   $152.60  
  Purchase #5 $51.85   7.870%   $55.9306   $55.93   $55.95   $55.90  
  Purchase #6 $228.38   11.681%   $255.0571   $255.06   $255.05   $255.10  
  Purchase #7 $209.46   8.266%   $226.774   $226.77   $226.75   $226.80  
  7 purchase totals = $882.26       $977.0535   $977.05   $977.05   $977.10