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 $122.58   3.391%   $126.7367   $126.74   $126.75   $126.70  
  Purchase #2 $88.55   11.106%   $98.3844   $98.38   $98.40   $98.40  
  Purchase #3 $115.37   6.836%   $123.2567   $123.26   $123.25   $123.30  
  Purchase #4 $216.89   11.224%   $241.2337   $241.23   $241.25   $241.20  
  Purchase #5 $228.97   12.123%   $256.728   $256.73   $256.75   $256.70  
  Purchase #6 $51.87   10.494%   $57.3132   $57.31   $57.30   $57.30  
  Purchase #7 $228.39   10.753%   $252.9488   $252.95   $252.95   $252.90  
  7 purchase totals = $1,052.62       $1,156.6015   $1,156.60   $1,156.65   $1,156.50