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 $56.81   11.587%   $63.3926   $63.39   $63.40   $63.40  
  Purchase #2 $196.52   7.634%   $211.5223   $211.52   $211.50   $211.50  
  Purchase #3 $62.48   3.257%   $64.515   $64.52   $64.50   $64.50  
  Purchase #4 $8.56   8.811%   $9.3142   $9.31   $9.30   $9.30  
  Purchase #5 $114.74   3.768%   $119.0634   $119.06   $119.05   $119.10  
  Purchase #6 $59.81   10.578%   $66.1367   $66.14   $66.15   $66.10  
  Purchase #7 $208.38   12.152%   $233.7023   $233.70   $233.70   $233.70  
  7 purchase totals = $707.30       $767.6465   $767.64   $767.60   $767.60