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 $244.41   9.768%   $268.284   $268.28   $268.30   $268.30  
  Purchase #2 $11.56   9.706%   $12.682   $12.68   $12.70   $12.70  
  Purchase #3 $44.39   11.589%   $49.5344   $49.53   $49.55   $49.50  
  Purchase #4 $156.65   7.541%   $168.463   $168.46   $168.45   $168.50  
  Purchase #5 $91.74   6.224%   $97.4499   $97.45   $97.45   $97.40  
  Purchase #6 $138.93   4.136%   $144.6761   $144.68   $144.70   $144.70  
  Purchase #7 $46.65   13.743%   $53.0611   $53.06   $53.05   $53.10  
  7 purchase totals = $734.33       $794.1505   $794.14   $794.20   $794.20