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 $126.65   4.112%   $131.8578   $131.86   $131.85   $131.90  
  Purchase #2 $119.72   11.396%   $133.3633   $133.36   $133.35   $133.40  
  Purchase #3 $15.74   6.543%   $16.7699   $16.77   $16.75   $16.80  
  Purchase #4 $174.67   9.231%   $190.7938   $190.79   $190.80   $190.80  
  Purchase #5 $230.69   13.304%   $261.381   $261.38   $261.40   $261.40  
  Purchase #6 $210.34   6.712%   $224.458   $224.46   $224.45   $224.50  
  Purchase #7 $79.31   12.746%   $89.4189   $89.42   $89.40   $89.40  
  7 purchase totals = $957.12       $1,048.0427   $1,048.04   $1,048.00   $1,048.20