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 $172.61   13.668%   $196.2023   $196.20   $196.20   $196.20  
  Purchase #2 $15.79   9.678%   $17.3182   $17.32   $17.30   $17.30  
  Purchase #3 $165.78   8.138%   $179.2712   $179.27   $179.25   $179.30  
  Purchase #4 $41.34   13.628%   $46.9738   $46.97   $46.95   $47.00  
  Purchase #5 $222.50   10.574%   $246.0272   $246.03   $246.05   $246.00  
  Purchase #6 $89.66   3.213%   $92.5408   $92.54   $92.55   $92.50  
  Purchase #7 $211.98   7.532%   $227.9463   $227.95   $227.95   $227.90  
  7 purchase totals = $919.66       $1,006.2798   $1,006.28   $1,006.25   $1,006.20