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 $235.80   10.361%   $260.2312   $260.23   $260.25   $260.20  
  Purchase #2 $91.93   7.325%   $98.6639   $98.66   $98.65   $98.70  
  Purchase #3 $184.38   12.102%   $206.6937   $206.69   $206.70   $206.70  
  Purchase #4 $206.61   7.722%   $222.5644   $222.56   $222.55   $222.60  
  Purchase #5 $198.92   6.859%   $212.5639   $212.56   $212.55   $212.60  
  Purchase #6 $85.54   8.285%   $92.627   $92.63   $92.65   $92.60  
  Purchase #7 $163.55   8.264%   $177.0658   $177.07   $177.05   $177.10  
  7 purchase totals = $1,166.73       $1,270.4099   $1,270.40   $1,270.40   $1,270.50