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 $82.70   11.767%   $92.4313   $92.43   $92.45   $92.40  
  Purchase #2 $55.64   6.475%   $59.2427   $59.24   $59.25   $59.20  
  Purchase #3 $212.85   10.402%   $234.9907   $234.99   $235.00   $235.00  
  Purchase #4 $242.60   7.604%   $261.0473   $261.05   $261.05   $261.00  
  Purchase #5 $235.29   5.781%   $248.8921   $248.89   $248.90   $248.90  
  Purchase #6 $16.99   12.127%   $19.0504   $19.05   $19.05   $19.10  
  Purchase #7 $229.83   12.538%   $258.6461   $258.65   $258.65   $258.60  
  7 purchase totals = $1,075.90       $1,174.3006   $1,174.30   $1,174.35   $1,174.20