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 $246.50   11.443%   $274.707   $274.71   $274.70   $274.70  
  Purchase #2 $58.66   10.360%   $64.7372   $64.74   $64.75   $64.70  
  Purchase #3 $136.89   7.272%   $146.8446   $146.84   $146.85   $146.80  
  Purchase #4 $41.50   11.837%   $46.4124   $46.41   $46.40   $46.40  
  Purchase #5 $101.45   5.382%   $106.91   $106.91   $106.90   $106.90  
  Purchase #6 $65.94   3.186%   $68.0408   $68.04   $68.05   $68.00  
  Purchase #7 $45.59   11.786%   $50.9632   $50.96   $50.95   $51.00  
  7 purchase totals = $696.53       $758.6152   $758.61   $758.60   $758.50