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 $118.94   12.873%   $134.2511   $134.25   $134.25   $134.30  
  Purchase #2 $104.91   9.570%   $114.9499   $114.95   $114.95   $114.90  
  Purchase #3 $20.99   6.540%   $22.3627   $22.36   $22.35   $22.40  
  Purchase #4 $160.35   4.218%   $167.1136   $167.11   $167.10   $167.10  
  Purchase #5 $154.49   7.229%   $165.6581   $165.66   $165.65   $165.70  
  Purchase #6 $208.94   13.266%   $236.658   $236.66   $236.65   $236.70  
  Purchase #7 $177.38   9.692%   $194.5717   $194.57   $194.55   $194.60  
  7 purchase totals = $946.00       $1,035.5651   $1,035.56   $1,035.50   $1,035.70