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 $137.63   3.390%   $142.2957   $142.30   $142.30   $142.30  
  Purchase #2 $66.54   13.694%   $75.652   $75.65   $75.65   $75.70  
  Purchase #3 $32.63   7.520%   $35.0838   $35.08   $35.10   $35.10  
  Purchase #4 $63.54   12.167%   $71.2709   $71.27   $71.25   $71.30  
  Purchase #5 $174.81   6.686%   $186.4978   $186.50   $186.50   $186.50  
  Purchase #6 $92.87   7.800%   $100.1139   $100.11   $100.10   $100.10  
  Purchase #7 $164.45   6.678%   $175.432   $175.43   $175.45   $175.40  
  7 purchase totals = $732.47       $786.3461   $786.34   $786.35   $786.40