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 $99.68   4.306%   $103.9722   $103.97   $103.95   $104.00  
  Purchase #2 $146.35   11.822%   $163.6515   $163.65   $163.65   $163.70  
  Purchase #3 $177.77   7.850%   $191.7249   $191.72   $191.70   $191.70  
  Purchase #4 $243.66   5.230%   $256.4034   $256.40   $256.40   $256.40  
  Purchase #5 $123.69   5.863%   $130.9419   $130.94   $130.95   $130.90  
  Purchase #6 $100.74   13.581%   $114.4215   $114.42   $114.40   $114.40  
  Purchase #7 $95.43   7.360%   $102.4536   $102.45   $102.45   $102.50  
  7 purchase totals = $987.32       $1,063.5690   $1,063.55   $1,063.50   $1,063.60