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 $191.53   5.464%   $201.9952   $202.00   $202.00   $202.00  
  Purchase #2 $157.74   6.583%   $168.124   $168.12   $168.10   $168.10  
  Purchase #3 $23.88   11.572%   $26.6434   $26.64   $26.65   $26.60  
  Purchase #4 $59.62   10.631%   $65.9582   $65.96   $65.95   $66.00  
  Purchase #5 $90.86   7.439%   $97.6191   $97.62   $97.60   $97.60  
  Purchase #6 $57.29   6.574%   $61.0562   $61.06   $61.05   $61.10  
  Purchase #7 $221.69   12.433%   $249.2527   $249.25   $249.25   $249.30  
  7 purchase totals = $802.61       $870.6488   $870.65   $870.60   $870.70