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 $184.31   9.116%   $201.1117   $201.11   $201.10   $201.10  
  Purchase #2 $32.70   3.353%   $33.7964   $33.80   $33.80   $33.80  
  Purchase #3 $207.99   10.434%   $229.6917   $229.69   $229.70   $229.70  
  Purchase #4 $68.38   13.792%   $77.811   $77.81   $77.80   $77.80  
  Purchase #5 $161.48   6.868%   $172.5704   $172.57   $172.55   $172.60  
  Purchase #6 $88.66   10.515%   $97.9826   $97.98   $98.00   $98.00  
  Purchase #7 $40.79   5.414%   $42.9984   $43.00   $43.00   $43.00  
  7 purchase totals = $784.31       $855.9622   $855.96   $855.95   $856.00