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 $63.55   6.610%   $67.7507   $67.75   $67.75   $67.80  
  Purchase #2 $223.39   11.333%   $248.7068   $248.71   $248.70   $248.70  
  Purchase #3 $201.63   4.515%   $210.7336   $210.73   $210.75   $210.70  
  Purchase #4 $133.94   8.458%   $145.2686   $145.27   $145.25   $145.30  
  Purchase #5 $52.48   11.309%   $58.415   $58.42   $58.40   $58.40  
  Purchase #6 $250.31   4.430%   $261.3987   $261.40   $261.40   $261.40  
  Purchase #7 $26.64   10.541%   $29.4481   $29.45   $29.45   $29.40  
  7 purchase totals = $951.94       $1,021.7215   $1,021.73   $1,021.70   $1,021.70