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 $154.87   12.523%   $174.2644   $174.26   $174.25   $174.30  
  Purchase #2 $188.93   6.846%   $201.8641   $201.86   $201.85   $201.90  
  Purchase #3 $66.92   13.849%   $76.1878   $76.19   $76.20   $76.20  
  Purchase #4 $60.87   3.464%   $62.9785   $62.98   $63.00   $63.00  
  Purchase #5 $124.76   7.181%   $133.719   $133.72   $133.70   $133.70  
  Purchase #6 $228.58   10.145%   $251.7694   $251.77   $251.75   $251.80  
  Purchase #7 $149.28   9.158%   $162.9511   $162.95   $162.95   $163.00  
  7 purchase totals = $974.21       $1,063.7343   $1,063.73   $1,063.70   $1,063.90