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 $91.46   4.812%   $95.8611   $95.86   $95.85   $95.90  
  Purchase #2 $127.81   4.857%   $134.0177   $134.02   $134.00   $134.00  
  Purchase #3 $176.57   3.627%   $182.9742   $182.97   $182.95   $183.00  
  Purchase #4 $222.35   6.269%   $236.2891   $236.29   $236.30   $236.30  
  Purchase #5 $136.94   4.330%   $142.8695   $142.87   $142.85   $142.90  
  Purchase #6 $25.45   8.108%   $27.5135   $27.51   $27.50   $27.50  
  Purchase #7 $31.34   8.678%   $34.0597   $34.06   $34.05   $34.10  
  7 purchase totals = $811.92       $853.5848   $853.58   $853.50   $853.70