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 $185.56   6.836%   $198.2449   $198.24   $198.25   $198.20  
  Purchase #2 $33.33   9.182%   $36.3904   $36.39   $36.40   $36.40  
  Purchase #3 $216.55   6.484%   $230.5911   $230.59   $230.60   $230.60  
  Purchase #4 $218.64   3.464%   $226.2137   $226.21   $226.20   $226.20  
  Purchase #5 $209.80   13.295%   $237.6929   $237.69   $237.70   $237.70  
  Purchase #6 $77.32   8.181%   $83.6455   $83.65   $83.65   $83.60  
  Purchase #7 $55.87   11.780%   $62.4515   $62.45   $62.45   $62.50  
  7 purchase totals = $997.07       $1,075.2300   $1,075.22   $1,075.25   $1,075.20