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 $41.68   10.761%   $46.1652   $46.17   $46.15   $46.20  
  Purchase #2 $134.61   3.550%   $139.3887   $139.39   $139.40   $139.40  
  Purchase #3 $181.69   11.134%   $201.9194   $201.92   $201.90   $201.90  
  Purchase #4 $224.26   10.825%   $248.5361   $248.54   $248.55   $248.50  
  Purchase #5 $22.99   7.655%   $24.7499   $24.75   $24.75   $24.70  
  Purchase #6 $80.87   12.837%   $91.2513   $91.25   $91.25   $91.30  
  Purchase #7 $58.87   11.387%   $65.5735   $65.57   $65.55   $65.60  
  7 purchase totals = $744.97       $817.5841   $817.59   $817.55   $817.60