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 $68.46   11.728%   $76.489   $76.49   $76.50   $76.50  
  Purchase #2 $84.54   3.277%   $87.3104   $87.31   $87.30   $87.30  
  Purchase #3 $45.70   8.252%   $49.4712   $49.47   $49.45   $49.50  
  Purchase #4 $224.57   8.866%   $244.4804   $244.48   $244.50   $244.50  
  Purchase #5 $228.47   10.418%   $252.272   $252.27   $252.25   $252.30  
  Purchase #6 $77.77   10.323%   $85.7982   $85.80   $85.80   $85.80  
  Purchase #7 $231.97   12.606%   $261.2121   $261.21   $261.20   $261.20  
  7 purchase totals = $961.48       $1,057.0333   $1,057.03   $1,057.00   $1,057.10