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 $247.91   5.504%   $261.555   $261.56   $261.55   $261.60  
  Purchase #2 $105.67   9.815%   $116.0415   $116.04   $116.05   $116.00  
  Purchase #3 $84.81   7.237%   $90.9477   $90.95   $90.95   $90.90  
  Purchase #4 $17.84   6.803%   $19.0537   $19.05   $19.05   $19.10  
  Purchase #5 $24.59   3.830%   $25.5318   $25.53   $25.55   $25.50  
  Purchase #6 $12.48   12.149%   $13.9962   $14.00   $14.00   $14.00  
  Purchase #7 $138.74   6.748%   $148.1022   $148.10   $148.10   $148.10  
  7 purchase totals = $632.04       $675.2281   $675.23   $675.25   $675.20