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 $32.47   8.638%   $35.2748   $35.27   $35.25   $35.30  
  Purchase #2 $200.84   8.392%   $217.6945   $217.69   $217.70   $217.70  
  Purchase #3 $162.73   10.502%   $179.8199   $179.82   $179.80   $179.80  
  Purchase #4 $159.25   13.383%   $180.5624   $180.56   $180.55   $180.60  
  Purchase #5 $226.66   6.367%   $241.0914   $241.09   $241.10   $241.10  
  Purchase #6 $71.56   6.774%   $76.4075   $76.41   $76.40   $76.40  
  Purchase #7 $73.25   11.325%   $81.5456   $81.55   $81.55   $81.50  
  7 purchase totals = $926.76       $1,012.3961   $1,012.39   $1,012.35   $1,012.40