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 $242.27   8.144%   $262.0005   $262.00   $262.00   $262.00  
  Purchase #2 $124.69   11.845%   $139.4595   $139.46   $139.45   $139.50  
  Purchase #3 $84.40   5.260%   $88.8394   $88.84   $88.85   $88.80  
  Purchase #4 $198.56   6.803%   $212.068   $212.07   $212.05   $212.10  
  Purchase #5 $17.30   11.215%   $19.2402   $19.24   $19.25   $19.20  
  Purchase #6 $243.44   8.488%   $264.1032   $264.10   $264.10   $264.10  
  Purchase #7 $76.93   11.217%   $85.5592   $85.56   $85.55   $85.60  
  7 purchase totals = $987.59       $1,071.2700   $1,071.27   $1,071.25   $1,071.30