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 $214.63   5.805%   $227.0893   $227.09   $227.10   $227.10  
  Purchase #2 $180.81   13.520%   $205.2555   $205.26   $205.25   $205.30  
  Purchase #3 $98.53   12.707%   $111.0502   $111.05   $111.05   $111.10  
  Purchase #4 $88.34   3.874%   $91.7623   $91.76   $91.75   $91.80  
  Purchase #5 $249.53   5.273%   $262.6877   $262.69   $262.70   $262.70  
  Purchase #6 $67.49   10.290%   $74.4347   $74.43   $74.45   $74.40  
  Purchase #7 $119.60   9.272%   $130.6893   $130.69   $130.70   $130.70  
  7 purchase totals = $1,018.93       $1,102.9690   $1,102.97   $1,103.00   $1,103.10