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 $217.93   10.724%   $241.3008   $241.30   $241.30   $241.30  
  Purchase #2 $162.44   11.798%   $181.6047   $181.60   $181.60   $181.60  
  Purchase #3 $245.37   3.121%   $253.028   $253.03   $253.05   $253.00  
  Purchase #4 $227.36   4.565%   $237.739   $237.74   $237.75   $237.70  
  Purchase #5 $51.60   7.865%   $55.6583   $55.66   $55.65   $55.70  
  Purchase #6 $56.37   5.334%   $59.3768   $59.38   $59.40   $59.40  
  Purchase #7 $181.43   11.366%   $202.0513   $202.05   $202.05   $202.10  
  7 purchase totals = $1,142.50       $1,230.7589   $1,230.76   $1,230.80   $1,230.80