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 $58.64   11.155%   $65.1813   $65.18   $65.20   $65.20  
  Purchase #2 $8.66   3.810%   $8.9899   $8.99   $9.00   $9.00  
  Purchase #3 $53.34   13.669%   $60.631   $60.63   $60.65   $60.60  
  Purchase #4 $39.88   11.550%   $44.4861   $44.49   $44.50   $44.50  
  Purchase #5 $48.42   8.744%   $52.6538   $52.65   $52.65   $52.70  
  Purchase #6 $31.81   13.355%   $36.0582   $36.06   $36.05   $36.10  
  Purchase #7 $52.50   8.533%   $56.9798   $56.98   $57.00   $57.00  
  7 purchase totals = $293.25       $324.9801   $324.98   $325.05   $325.10