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 $148.99   10.465%   $164.5818   $164.58   $164.60   $164.60  
  Purchase #2 $54.32   9.630%   $59.551   $59.55   $59.55   $59.60  
  Purchase #3 $44.62   8.616%   $48.4645   $48.46   $48.45   $48.50  
  Purchase #4 $56.39   3.867%   $58.5706   $58.57   $58.55   $58.60  
  Purchase #5 $102.72   12.232%   $115.2847   $115.28   $115.30   $115.30  
  Purchase #6 $65.85   9.619%   $72.1841   $72.18   $72.20   $72.20  
  Purchase #7 $229.38   13.524%   $260.4014   $260.40   $260.40   $260.40  
  7 purchase totals = $702.27       $779.0381   $779.02   $779.05   $779.20