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 $59.83   9.202%   $65.3356   $65.34   $65.35   $65.30  
  Purchase #2 $88.45   9.772%   $97.0933   $97.09   $97.10   $97.10  
  Purchase #3 $13.81   10.155%   $15.2124   $15.21   $15.20   $15.20  
  Purchase #4 $55.88   12.422%   $62.8214   $62.82   $62.80   $62.80  
  Purchase #5 $248.76   9.748%   $273.0091   $273.01   $273.00   $273.00  
  Purchase #6 $155.59   12.241%   $174.6358   $174.64   $174.65   $174.60  
  Purchase #7 $167.53   12.647%   $188.7175   $188.72   $188.70   $188.70  
  7 purchase totals = $789.85       $876.8251   $876.83   $876.80   $876.70