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 $191.54   5.451%   $201.9808   $201.98   $202.00   $202.00  
  Purchase #2 $185.39   8.538%   $201.2186   $201.22   $201.20   $201.20  
  Purchase #3 $171.45   13.110%   $193.9271   $193.93   $193.95   $193.90  
  Purchase #4 $237.81   11.551%   $265.2794   $265.28   $265.30   $265.30  
  Purchase #5 $45.42   13.636%   $51.6135   $51.61   $51.60   $51.60  
  Purchase #6 $59.26   10.296%   $65.3614   $65.36   $65.35   $65.40  
  Purchase #7 $16.31   11.347%   $18.1607   $18.16   $18.15   $18.20  
  7 purchase totals = $907.18       $997.5415   $997.54   $997.55   $997.60