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 $193.85   4.197%   $201.9859   $201.99   $202.00   $202.00  
  Purchase #2 $48.57   12.102%   $54.4479   $54.45   $54.45   $54.40  
  Purchase #3 $237.41   8.699%   $258.0623   $258.06   $258.05   $258.10  
  Purchase #4 $30.35   11.627%   $33.8788   $33.88   $33.90   $33.90  
  Purchase #5 $183.69   9.764%   $201.6255   $201.63   $201.65   $201.60  
  Purchase #6 $5.27   6.832%   $5.63   $5.63   $5.65   $5.60  
  Purchase #7 $185.74   11.663%   $207.4029   $207.40   $207.40   $207.40  
  7 purchase totals = $884.88       $963.0333   $963.04   $963.10   $963.00