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 $106.63   3.109%   $109.9451   $109.95   $109.95   $109.90  
  Purchase #2 $195.38   3.725%   $202.6579   $202.66   $202.65   $202.70  
  Purchase #3 $81.66   6.661%   $87.0994   $87.10   $87.10   $87.10  
  Purchase #4 $114.96   10.378%   $126.8905   $126.89   $126.90   $126.90  
  Purchase #5 $237.56   10.624%   $262.7984   $262.80   $262.80   $262.80  
  Purchase #6 $118.61   3.596%   $122.8752   $122.88   $122.90   $122.90  
  Purchase #7 $26.53   11.392%   $29.5523   $29.55   $29.55   $29.60  
  7 purchase totals = $881.33       $941.8188   $941.83   $941.85   $941.90