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 $113.88   11.273%   $126.7177   $126.72   $126.70   $126.70  
  Purchase #2 $169.37   11.400%   $188.6782   $188.68   $188.70   $188.70  
  Purchase #3 $140.36   4.157%   $146.1948   $146.19   $146.20   $146.20  
  Purchase #4 $166.54   5.529%   $175.748   $175.75   $175.75   $175.70  
  Purchase #5 $209.36   12.748%   $236.0492   $236.05   $236.05   $236.00  
  Purchase #6 $63.37   3.300%   $65.4612   $65.46   $65.45   $65.50  
  Purchase #7 $83.86   10.695%   $92.8288   $92.83   $92.85   $92.80  
  7 purchase totals = $946.74       $1,031.6779   $1,031.68   $1,031.70   $1,031.60