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 $34.83   10.338%   $38.4307   $38.43   $38.45   $38.40  
  Purchase #2 $119.33   13.389%   $135.3071   $135.31   $135.30   $135.30  
  Purchase #3 $51.47   4.308%   $53.6873   $53.69   $53.70   $53.70  
  Purchase #4 $212.58   5.824%   $224.9607   $224.96   $224.95   $225.00  
  Purchase #5 $242.78   3.363%   $250.9447   $250.94   $250.95   $250.90  
  Purchase #6 $102.92   6.198%   $109.299   $109.30   $109.30   $109.30  
  Purchase #7 $196.56   10.327%   $216.8588   $216.86   $216.85   $216.90  
  7 purchase totals = $960.47       $1,029.4883   $1,029.49   $1,029.50   $1,029.50