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 $129.42   13.210%   $146.5164   $146.52   $146.50   $146.50  
  Purchase #2 $63.44   8.696%   $68.9567   $68.96   $68.95   $69.00  
  Purchase #3 $185.77   4.151%   $193.4813   $193.48   $193.50   $193.50  
  Purchase #4 $76.58   5.387%   $80.7054   $80.71   $80.70   $80.70  
  Purchase #5 $52.52   4.517%   $54.8923   $54.89   $54.90   $54.90  
  Purchase #6 $106.92   13.390%   $121.2366   $121.24   $121.25   $121.20  
  Purchase #7 $236.36   12.864%   $266.7654   $266.77   $266.75   $266.80  
  7 purchase totals = $851.01       $932.5541   $932.57   $932.55   $932.60