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 $29.57   8.506%   $32.0852   $32.09   $32.10   $32.10  
  Purchase #2 $113.95   12.699%   $128.4205   $128.42   $128.40   $128.40  
  Purchase #3 $94.81   8.276%   $102.6565   $102.66   $102.65   $102.70  
  Purchase #4 $174.87   7.517%   $188.015   $188.02   $188.00   $188.00  
  Purchase #5 $193.80   6.596%   $206.583   $206.58   $206.60   $206.60  
  Purchase #6 $172.28   6.663%   $183.759   $183.76   $183.75   $183.80  
  Purchase #7 $48.88   12.869%   $55.1704   $55.17   $55.15   $55.20  
  7 purchase totals = $828.16       $896.6896   $896.70   $896.65   $896.80