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 $208.86   11.430%   $232.7327   $232.73   $232.75   $232.70  
  Purchase #2 $67.47   13.786%   $76.7714   $76.77   $76.75   $76.80  
  Purchase #3 $33.76   7.400%   $36.2582   $36.26   $36.25   $36.30  
  Purchase #4 $94.84   13.803%   $107.9308   $107.93   $107.95   $107.90  
  Purchase #5 $21.77   9.569%   $23.8532   $23.85   $23.85   $23.90  
  Purchase #6 $110.44   10.726%   $122.2858   $122.29   $122.30   $122.30  
  Purchase #7 $181.64   5.644%   $191.8918   $191.89   $191.90   $191.90  
  7 purchase totals = $718.78       $791.7239   $791.72   $791.75   $791.80