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 $182.44   6.122%   $193.609   $193.61   $193.60   $193.60  
  Purchase #2 $213.89   11.736%   $238.9921   $238.99   $239.00   $239.00  
  Purchase #3 $136.91   7.154%   $146.7045   $146.70   $146.70   $146.70  
  Purchase #4 $78.94   3.829%   $81.9626   $81.96   $81.95   $82.00  
  Purchase #5 $48.62   8.299%   $52.655   $52.66   $52.65   $52.70  
  Purchase #6 $207.62   13.816%   $236.3048   $236.30   $236.30   $236.30  
  Purchase #7 $98.45   11.796%   $110.0632   $110.06   $110.05   $110.10  
  7 purchase totals = $966.87       $1,060.2912   $1,060.28   $1,060.25   $1,060.40