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 $238.32   12.641%   $268.446   $268.45   $268.45   $268.40  
  Purchase #2 $217.26   4.867%   $227.834   $227.83   $227.85   $227.80  
  Purchase #3 $95.90   4.472%   $100.1886   $100.19   $100.20   $100.20  
  Purchase #4 $67.92   5.128%   $71.4029   $71.40   $71.40   $71.40  
  Purchase #5 $43.71   8.721%   $47.5219   $47.52   $47.50   $47.50  
  Purchase #6 $8.80   4.661%   $9.2102   $9.21   $9.20   $9.20  
  Purchase #7 $209.48   12.543%   $235.7551   $235.76   $235.75   $235.80  
  7 purchase totals = $881.39       $960.3587   $960.36   $960.35   $960.30