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 $245.95   6.546%   $262.0499   $262.05   $262.05   $262.00  
  Purchase #2 $17.30   11.428%   $19.277   $19.28   $19.30   $19.30  
  Purchase #3 $64.87   10.298%   $71.5503   $71.55   $71.55   $71.60  
  Purchase #4 $190.55   4.309%   $198.7608   $198.76   $198.75   $198.80  
  Purchase #5 $100.58   9.762%   $110.3986   $110.40   $110.40   $110.40  
  Purchase #6 $59.66   7.435%   $64.0957   $64.10   $64.10   $64.10  
  Purchase #7 $119.64   3.260%   $123.5403   $123.54   $123.55   $123.50  
  7 purchase totals = $798.55       $849.6726   $849.68   $849.70   $849.70