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 $89.84   5.195%   $94.5072   $94.51   $94.50   $94.50  
  Purchase #2 $58.48   11.574%   $65.2485   $65.25   $65.25   $65.20  
  Purchase #3 $72.53   4.305%   $75.6524   $75.65   $75.65   $75.70  
  Purchase #4 $155.46   3.605%   $161.0643   $161.06   $161.05   $161.10  
  Purchase #5 $191.96   11.156%   $213.3751   $213.38   $213.40   $213.40  
  Purchase #6 $39.96   4.848%   $41.8973   $41.90   $41.90   $41.90  
  Purchase #7 $110.69   10.456%   $122.2637   $122.26   $122.25   $122.30  
  7 purchase totals = $718.92       $774.0085   $774.01   $774.00   $774.10