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 $120.87   5.706%   $127.7668   $127.77   $127.75   $127.80  
  Purchase #2 $106.83   7.332%   $114.6628   $114.66   $114.65   $114.70  
  Purchase #3 $49.89   7.605%   $53.6841   $53.68   $53.70   $53.70  
  Purchase #4 $42.77   12.814%   $48.2505   $48.25   $48.25   $48.30  
  Purchase #5 $227.73   6.538%   $242.619   $242.62   $242.60   $242.60  
  Purchase #6 $29.51   12.654%   $33.2442   $33.24   $33.25   $33.20  
  Purchase #7 $226.31   6.841%   $241.7919   $241.79   $241.80   $241.80  
  7 purchase totals = $803.91       $862.0193   $862.01   $862.00   $862.10