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 $206.76   5.128%   $217.3627   $217.36   $217.35   $217.40  
  Purchase #2 $34.62   11.553%   $38.6196   $38.62   $38.60   $38.60  
  Purchase #3 $68.32   7.755%   $73.6182   $73.62   $73.60   $73.60  
  Purchase #4 $41.28   4.674%   $43.2094   $43.21   $43.20   $43.20  
  Purchase #5 $242.37   3.193%   $250.1089   $250.11   $250.10   $250.10  
  Purchase #6 $240.30   3.480%   $248.6624   $248.66   $248.65   $248.70  
  Purchase #7 $225.79   7.523%   $242.7762   $242.78   $242.80   $242.80  
  7 purchase totals = $1,059.44       $1,114.3574   $1,114.36   $1,114.30   $1,114.40