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 $135.95   7.816%   $146.5759   $146.58   $146.60   $146.60  
  Purchase #2 $241.83   8.874%   $263.29   $263.29   $263.30   $263.30  
  Purchase #3 $75.44   7.683%   $81.2361   $81.24   $81.25   $81.20  
  Purchase #4 $208.69   7.618%   $224.588   $224.59   $224.60   $224.60  
  Purchase #5 $22.57   9.383%   $24.6877   $24.69   $24.70   $24.70  
  Purchase #6 $123.32   11.417%   $137.3994   $137.40   $137.40   $137.40  
  Purchase #7 $38.95   6.712%   $41.5643   $41.56   $41.55   $41.60  
  7 purchase totals = $846.75       $919.3414   $919.35   $919.40   $919.40