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 $76.41   6.282%   $81.2101   $81.21   $81.20   $81.20  
  Purchase #2 $234.38   9.590%   $256.857   $256.86   $256.85   $256.90  
  Purchase #3 $41.64   8.202%   $45.0553   $45.06   $45.05   $45.10  
  Purchase #4 $70.79   12.395%   $79.5644   $79.56   $79.55   $79.60  
  Purchase #5 $102.85   6.720%   $109.7615   $109.76   $109.75   $109.80  
  Purchase #6 $230.26   4.764%   $241.2296   $241.23   $241.25   $241.20  
  Purchase #7 $236.64   10.571%   $261.6552   $261.66   $261.65   $261.70  
  7 purchase totals = $992.97       $1,075.3331   $1,075.34   $1,075.30   $1,075.50