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 $195.66   6.790%   $208.9453   $208.95   $208.95   $208.90  
  Purchase #2 $86.32   13.358%   $97.8506   $97.85   $97.85   $97.90  
  Purchase #3 $173.89   5.563%   $183.5635   $183.56   $183.55   $183.60  
  Purchase #4 $75.67   12.336%   $85.0047   $85.00   $85.00   $85.00  
  Purchase #5 $124.62   12.857%   $140.6424   $140.64   $140.65   $140.60  
  Purchase #6 $53.97   12.539%   $60.7373   $60.74   $60.75   $60.70  
  Purchase #7 $78.69   7.636%   $84.6988   $84.70   $84.70   $84.70  
  7 purchase totals = $788.82       $861.4426   $861.44   $861.45   $861.40