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 $89.93   9.466%   $98.4428   $98.44   $98.45   $98.40  
  Purchase #2 $207.49   10.129%   $228.5067   $228.51   $228.50   $228.50  
  Purchase #3 $96.25   12.222%   $108.0137   $108.01   $108.00   $108.00  
  Purchase #4 $192.99   4.436%   $201.551   $201.55   $201.55   $201.60  
  Purchase #5 $179.59   9.236%   $196.1769   $196.18   $196.20   $196.20  
  Purchase #6 $59.38   11.856%   $66.4201   $66.42   $66.40   $66.40  
  Purchase #7 $57.51   8.715%   $62.522   $62.52   $62.50   $62.50  
  7 purchase totals = $883.14       $961.6332   $961.63   $961.60   $961.60