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 $24.32   9.139%   $26.5426   $26.54   $26.55   $26.50  
  Purchase #2 $107.53   7.696%   $115.8055   $115.81   $115.80   $115.80  
  Purchase #3 $219.61   9.638%   $240.776   $240.78   $240.80   $240.80  
  Purchase #4 $235.70   11.355%   $262.4637   $262.46   $262.45   $262.50  
  Purchase #5 $207.99   3.783%   $215.8583   $215.86   $215.85   $215.90  
  Purchase #6 $116.59   6.767%   $124.4796   $124.48   $124.50   $124.50  
  Purchase #7 $44.95   8.799%   $48.9052   $48.91   $48.90   $48.90  
  7 purchase totals = $956.69       $1,034.8309   $1,034.84   $1,034.85   $1,034.90