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 $39.76   5.663%   $42.0116   $42.01   $42.00   $42.00  
  Purchase #2 $222.93   6.626%   $237.7013   $237.70   $237.70   $237.70  
  Purchase #3 $248.69   5.264%   $261.781   $261.78   $261.80   $261.80  
  Purchase #4 $236.34   11.695%   $263.98   $263.98   $264.00   $264.00  
  Purchase #5 $37.99   11.735%   $42.4481   $42.45   $42.45   $42.40  
  Purchase #6 $209.52   9.711%   $229.8665   $229.87   $229.85   $229.90  
  Purchase #7 $184.94   3.224%   $190.9025   $190.90   $190.90   $190.90  
  7 purchase totals = $1,180.17       $1,268.6910   $1,268.69   $1,268.70   $1,268.70