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 $228.27   8.706%   $248.1432   $248.14   $248.15   $248.10  
  Purchase #2 $62.93   12.586%   $70.8504   $70.85   $70.85   $70.90  
  Purchase #3 $165.39   6.233%   $175.6988   $175.70   $175.70   $175.70  
  Purchase #4 $43.30   8.272%   $46.8818   $46.88   $46.90   $46.90  
  Purchase #5 $66.72   6.439%   $71.0161   $71.02   $71.00   $71.00  
  Purchase #6 $102.41   12.186%   $114.8897   $114.89   $114.90   $114.90  
  Purchase #7 $187.44   8.115%   $202.6508   $202.65   $202.65   $202.70  
  7 purchase totals = $856.46       $930.1308   $930.13   $930.15   $930.20