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 $246.73   10.221%   $271.9483   $271.95   $271.95   $271.90  
  Purchase #2 $248.76   5.418%   $262.2378   $262.24   $262.25   $262.20  
  Purchase #3 $223.83   13.481%   $254.0045   $254.00   $254.00   $254.00  
  Purchase #4 $14.71   6.455%   $15.6595   $15.66   $15.65   $15.70  
  Purchase #5 $89.80   8.674%   $97.5893   $97.59   $97.60   $97.60  
  Purchase #6 $53.46   9.596%   $58.59   $58.59   $58.60   $58.60  
  Purchase #7 $139.73   4.810%   $146.451   $146.45   $146.45   $146.50  
  7 purchase totals = $1,017.02       $1,106.4804   $1,106.48   $1,106.50   $1,106.50