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 $196.70   11.212%   $218.754   $218.75   $218.75   $218.80  
  Purchase #2 $58.36   13.562%   $66.2748   $66.27   $66.25   $66.30  
  Purchase #3 $61.35   8.587%   $66.6181   $66.62   $66.60   $66.60  
  Purchase #4 $100.60   8.311%   $108.9609   $108.96   $108.95   $109.00  
  Purchase #5 $176.45   9.693%   $193.5533   $193.55   $193.55   $193.60  
  Purchase #6 $80.63   12.446%   $90.6652   $90.67   $90.65   $90.70  
  Purchase #7 $232.68   12.482%   $261.7231   $261.72   $261.70   $261.70  
  7 purchase totals = $906.77       $1,006.5494   $1,006.54   $1,006.45   $1,006.70