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 $139.72   4.497%   $146.0032   $146.00   $146.00   $146.00  
  Purchase #2 $114.29   9.125%   $124.719   $124.72   $124.70   $124.70  
  Purchase #3 $198.27   6.477%   $211.1119   $211.11   $211.10   $211.10  
  Purchase #4 $19.77   12.197%   $22.1813   $22.18   $22.20   $22.20  
  Purchase #5 $141.91   11.510%   $158.2438   $158.24   $158.25   $158.20  
  Purchase #6 $68.51   12.585%   $77.132   $77.13   $77.15   $77.10  
  Purchase #7 $43.54   13.615%   $49.468   $49.47   $49.45   $49.50  
  7 purchase totals = $726.01       $788.8592   $788.85   $788.85   $788.80