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 $195.44   6.427%   $208.0009   $208.00   $208.00   $208.00  
  Purchase #2 $129.27   13.387%   $146.5754   $146.58   $146.60   $146.60  
  Purchase #3 $228.64   3.689%   $237.0745   $237.07   $237.05   $237.10  
  Purchase #4 $169.27   3.632%   $175.4179   $175.42   $175.40   $175.40  
  Purchase #5 $130.35   4.760%   $136.5547   $136.55   $136.55   $136.60  
  Purchase #6 $58.47   9.337%   $63.9293   $63.93   $63.95   $63.90  
  Purchase #7 $115.33   9.840%   $126.6785   $126.68   $126.70   $126.70  
  7 purchase totals = $1,026.77       $1,094.2312   $1,094.23   $1,094.25   $1,094.30