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 $59.39   9.488%   $65.0249   $65.02   $65.00   $65.00  
  Purchase #2 $113.28   8.407%   $122.8034   $122.80   $122.80   $122.80  
  Purchase #3 $93.44   5.596%   $98.6689   $98.67   $98.65   $98.70  
  Purchase #4 $101.37   7.329%   $108.7994   $108.80   $108.80   $108.80  
  Purchase #5 $72.87   6.478%   $77.5905   $77.59   $77.60   $77.60  
  Purchase #6 $208.59   13.192%   $236.1072   $236.11   $236.10   $236.10  
  Purchase #7 $248.57   6.226%   $264.046   $264.05   $264.05   $264.00  
  7 purchase totals = $897.51       $973.0403   $973.04   $973.00   $973.00