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 $114.38   10.257%   $126.112   $126.11   $126.10   $126.10  
  Purchase #2 $52.62   9.703%   $57.7257   $57.73   $57.75   $57.70  
  Purchase #3 $100.88   13.112%   $114.1074   $114.11   $114.10   $114.10  
  Purchase #4 $64.66   6.797%   $69.0549   $69.05   $69.05   $69.10  
  Purchase #5 $85.39   4.715%   $89.4161   $89.42   $89.40   $89.40  
  Purchase #6 $115.59   6.805%   $123.4559   $123.46   $123.45   $123.50  
  Purchase #7 $24.39   5.334%   $25.691   $25.69   $25.70   $25.70  
  7 purchase totals = $557.91       $605.5630   $605.57   $605.55   $605.60