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 $243.56   6.636%   $259.7226   $259.72   $259.70   $259.70  
  Purchase #2 $110.85   13.189%   $125.47   $125.47   $125.45   $125.50  
  Purchase #3 $71.66   3.586%   $74.2297   $74.23   $74.25   $74.20  
  Purchase #4 $33.99   3.137%   $35.0563   $35.06   $35.05   $35.10  
  Purchase #5 $228.53   6.603%   $243.6198   $243.62   $243.60   $243.60  
  Purchase #6 $225.56   10.138%   $248.4273   $248.43   $248.45   $248.40  
  Purchase #7 $23.50   9.332%   $25.693   $25.69   $25.70   $25.70  
  7 purchase totals = $937.65       $1,012.2187   $1,012.22   $1,012.20   $1,012.20