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 $211.90   11.660%   $236.6075   $236.61   $236.60   $236.60  
  Purchase #2 $54.77   9.183%   $59.7995   $59.80   $59.80   $59.80  
  Purchase #3 $147.25   8.790%   $160.1933   $160.19   $160.20   $160.20  
  Purchase #4 $156.93   12.388%   $176.3705   $176.37   $176.35   $176.40  
  Purchase #5 $48.70   8.665%   $52.9199   $52.92   $52.90   $52.90  
  Purchase #6 $131.45   4.385%   $137.2141   $137.21   $137.20   $137.20  
  Purchase #7 $38.84   13.515%   $44.0892   $44.09   $44.10   $44.10  
  7 purchase totals = $789.84       $867.1940   $867.19   $867.15   $867.20