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 $66.49   10.430%   $73.4249   $73.42   $73.40   $73.40  
  Purchase #2 $245.68   6.501%   $261.6517   $261.65   $261.65   $261.70  
  Purchase #3 $196.72   13.400%   $223.0805   $223.08   $223.10   $223.10  
  Purchase #4 $76.29   10.357%   $84.1914   $84.19   $84.20   $84.20  
  Purchase #5 $191.97   4.785%   $201.1558   $201.16   $201.15   $201.20  
  Purchase #6 $151.26   4.288%   $157.746   $157.75   $157.75   $157.70  
  Purchase #7 $38.28   12.171%   $42.9391   $42.94   $42.95   $42.90  
  7 purchase totals = $966.69       $1,044.1894   $1,044.19   $1,044.20   $1,044.20