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 $241.55   7.866%   $260.5503   $260.55   $260.55   $260.60  
  Purchase #2 $55.74   6.203%   $59.1976   $59.20   $59.20   $59.20  
  Purchase #3 $183.25   8.526%   $198.8739   $198.87   $198.85   $198.90  
  Purchase #4 $54.58   4.807%   $57.2037   $57.20   $57.20   $57.20  
  Purchase #5 $29.80   10.491%   $32.9263   $32.93   $32.95   $32.90  
  Purchase #6 $240.61   6.409%   $256.0307   $256.03   $256.05   $256.00  
  Purchase #7 $243.70   3.177%   $251.4423   $251.44   $251.45   $251.40  
  7 purchase totals = $1,049.23       $1,116.2248   $1,116.22   $1,116.25   $1,116.20