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 $183.51   10.621%   $203.0006   $203.00   $203.00   $203.00  
  Purchase #2 $156.64   5.122%   $164.6631   $164.66   $164.65   $164.70  
  Purchase #3 $180.70   7.655%   $194.5326   $194.53   $194.55   $194.50  
  Purchase #4 $177.44   7.254%   $190.3115   $190.31   $190.30   $190.30  
  Purchase #5 $43.42   9.858%   $47.7003   $47.70   $47.70   $47.70  
  Purchase #6 $188.54   6.697%   $201.1665   $201.17   $201.15   $201.20  
  Purchase #7 $171.95   12.391%   $193.2563   $193.26   $193.25   $193.30  
  7 purchase totals = $1,102.20       $1,194.6309   $1,194.63   $1,194.60   $1,194.70