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 $104.78   9.682%   $114.9248   $114.92   $114.90   $114.90  
  Purchase #2 $174.46   8.313%   $188.9629   $188.96   $188.95   $189.00  
  Purchase #3 $161.59   8.697%   $175.6435   $175.64   $175.65   $175.60  
  Purchase #4 $32.59   7.664%   $35.0877   $35.09   $35.10   $35.10  
  Purchase #5 $207.64   9.267%   $226.882   $226.88   $226.90   $226.90  
  Purchase #6 $194.52   10.828%   $215.5826   $215.58   $215.60   $215.60  
  Purchase #7 $68.42   6.506%   $72.8714   $72.87   $72.85   $72.90  
  7 purchase totals = $944.00       $1,029.9549   $1,029.94   $1,029.95   $1,030.00