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 $50.36   11.103%   $55.9515   $55.95   $55.95   $56.00  
  Purchase #2 $15.90   4.790%   $16.6616   $16.66   $16.65   $16.70  
  Purchase #3 $215.53   10.751%   $238.7016   $238.70   $238.70   $238.70  
  Purchase #4 $75.74   13.671%   $86.0944   $86.09   $86.10   $86.10  
  Purchase #5 $45.29   3.760%   $46.9929   $46.99   $47.00   $47.00  
  Purchase #6 $171.70   12.738%   $193.5711   $193.57   $193.55   $193.60  
  Purchase #7 $202.63   10.594%   $224.0966   $224.10   $224.10   $224.10  
  7 purchase totals = $777.15       $862.0697   $862.06   $862.05   $862.20