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 $59.75   8.756%   $64.9817   $64.98   $65.00   $65.00  
  Purchase #2 $134.47   3.810%   $139.5933   $139.59   $139.60   $139.60  
  Purchase #3 $9.70   13.108%   $10.9715   $10.97   $10.95   $11.00  
  Purchase #4 $247.68   10.593%   $273.9167   $273.92   $273.90   $273.90  
  Purchase #5 $160.31   10.127%   $176.5446   $176.54   $176.55   $176.50  
  Purchase #6 $65.77   11.824%   $73.5466   $73.55   $73.55   $73.50  
  Purchase #7 $224.40   9.708%   $246.1848   $246.18   $246.20   $246.20  
  7 purchase totals = $902.08       $985.7392   $985.73   $985.75   $985.70