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 $177.76   11.462%   $198.1349   $198.13   $198.15   $198.10  
  Purchase #2 $224.70   7.687%   $241.9727   $241.97   $241.95   $242.00  
  Purchase #3 $73.78   11.458%   $82.2337   $82.23   $82.25   $82.20  
  Purchase #4 $237.46   5.786%   $251.1994   $251.20   $251.20   $251.20  
  Purchase #5 $241.36   9.473%   $264.224   $264.22   $264.20   $264.20  
  Purchase #6 $75.73   3.485%   $78.3692   $78.37   $78.35   $78.40  
  Purchase #7 $153.73   11.583%   $171.5365   $171.54   $171.55   $171.50  
  7 purchase totals = $1,184.52       $1,287.6704   $1,287.66   $1,287.65   $1,287.60