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 $100.66   13.691%   $114.4414   $114.44   $114.45   $114.40  
  Purchase #2 $193.53   12.522%   $217.7638   $217.76   $217.75   $217.80  
  Purchase #3 $216.98   5.276%   $228.4279   $228.43   $228.45   $228.40  
  Purchase #4 $96.60   5.337%   $101.7555   $101.76   $101.75   $101.80  
  Purchase #5 $162.76   10.213%   $179.3827   $179.38   $179.40   $179.40  
  Purchase #6 $46.65   12.619%   $52.5368   $52.54   $52.55   $52.50  
  Purchase #7 $113.45   13.599%   $128.8781   $128.88   $128.90   $128.90  
  7 purchase totals = $930.63       $1,023.1862   $1,023.19   $1,023.25   $1,023.20