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 $74.89   13.379%   $84.9095   $84.91   $84.90   $84.90  
  Purchase #2 $170.87   4.869%   $179.1897   $179.19   $179.20   $179.20  
  Purchase #3 $244.46   4.684%   $255.9105   $255.91   $255.90   $255.90  
  Purchase #4 $51.54   12.596%   $58.032   $58.03   $58.05   $58.00  
  Purchase #5 $224.99   10.480%   $248.569   $248.57   $248.55   $248.60  
  Purchase #6 $9.87   11.618%   $11.0167   $11.02   $11.00   $11.00  
  Purchase #7 $211.81   8.580%   $229.9833   $229.98   $230.00   $230.00  
  7 purchase totals = $988.43       $1,067.6107   $1,067.61   $1,067.60   $1,067.60