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 $92.79   13.254%   $105.0884   $105.09   $105.10   $105.10  
  Purchase #2 $104.42   9.793%   $114.6459   $114.65   $114.65   $114.60  
  Purchase #3 $110.73   8.254%   $119.8697   $119.87   $119.85   $119.90  
  Purchase #4 $234.41   11.722%   $261.8875   $261.89   $261.90   $261.90  
  Purchase #5 $145.67   13.354%   $165.1228   $165.12   $165.10   $165.10  
  Purchase #6 $6.38   3.455%   $6.6004   $6.60   $6.60   $6.60  
  Purchase #7 $166.80   13.787%   $189.7967   $189.80   $189.80   $189.80  
  7 purchase totals = $861.20       $963.0114   $963.02   $963.00   $963.00