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 $224.37   11.512%   $250.1995   $250.20   $250.20   $250.20  
  Purchase #2 $129.53   4.491%   $135.3472   $135.35   $135.35   $135.30  
  Purchase #3 $241.47   10.717%   $267.3483   $267.35   $267.35   $267.30  
  Purchase #4 $176.86   5.632%   $186.8208   $186.82   $186.80   $186.80  
  Purchase #5 $35.34   6.335%   $37.5788   $37.58   $37.60   $37.60  
  Purchase #6 $221.91   13.183%   $251.1644   $251.16   $251.15   $251.20  
  Purchase #7 $227.27   4.796%   $238.1699   $238.17   $238.15   $238.20  
  7 purchase totals = $1,256.75       $1,366.6289   $1,366.63   $1,366.60   $1,366.60