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 $209.69   10.684%   $232.0933   $232.09   $232.10   $232.10  
  Purchase #2 $82.26   13.376%   $93.2631   $93.26   $93.25   $93.30  
  Purchase #3 $118.42   5.295%   $124.6903   $124.69   $124.70   $124.70  
  Purchase #4 $111.88   4.656%   $117.0891   $117.09   $117.10   $117.10  
  Purchase #5 $26.89   6.118%   $28.5351   $28.54   $28.55   $28.50  
  Purchase #6 $183.71   12.824%   $207.269   $207.27   $207.25   $207.30  
  Purchase #7 $244.89   8.702%   $266.2003   $266.20   $266.20   $266.20  
  7 purchase totals = $977.74       $1,069.1402   $1,069.14   $1,069.15   $1,069.20