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 $212.92   8.680%   $231.4015   $231.40   $231.40   $231.40  
  Purchase #2 $221.41   7.413%   $237.8231   $237.82   $237.80   $237.80  
  Purchase #3 $162.54   10.472%   $179.5612   $179.56   $179.55   $179.60  
  Purchase #4 $20.78   12.709%   $23.4209   $23.42   $23.40   $23.40  
  Purchase #5 $207.56   5.476%   $218.926   $218.93   $218.95   $218.90  
  Purchase #6 $55.54   5.732%   $58.7236   $58.72   $58.70   $58.70  
  Purchase #7 $72.80   11.455%   $81.1392   $81.14   $81.15   $81.10  
  7 purchase totals = $953.55       $1,030.9955   $1,030.99   $1,030.95   $1,030.90