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 $47.78   12.143%   $53.5819   $53.58   $53.60   $53.60  
  Purchase #2 $228.86   9.692%   $251.0411   $251.04   $251.05   $251.00  
  Purchase #3 $141.31   11.207%   $157.1466   $157.15   $157.15   $157.10  
  Purchase #4 $119.56   13.332%   $135.4997   $135.50   $135.50   $135.50  
  Purchase #5 $196.49   12.557%   $221.1632   $221.16   $221.15   $221.20  
  Purchase #6 $26.49   6.285%   $28.1549   $28.15   $28.15   $28.20  
  Purchase #7 $186.33   3.757%   $193.3304   $193.33   $193.35   $193.30  
  7 purchase totals = $946.82       $1,039.9178   $1,039.91   $1,039.95   $1,039.90