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 $241.28   7.359%   $259.0358   $259.04   $259.05   $259.00  
  Purchase #2 $72.97   4.308%   $76.1135   $76.11   $76.10   $76.10  
  Purchase #3 $166.91   11.792%   $186.592   $186.59   $186.60   $186.60  
  Purchase #4 $209.47   12.464%   $235.5783   $235.58   $235.60   $235.60  
  Purchase #5 $200.89   8.167%   $217.2967   $217.30   $217.30   $217.30  
  Purchase #6 $131.28   5.405%   $138.3757   $138.38   $138.40   $138.40  
  Purchase #7 $16.66   11.459%   $18.5691   $18.57   $18.55   $18.60  
  7 purchase totals = $1,039.46       $1,131.5611   $1,131.57   $1,131.60   $1,131.60