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 $160.26   11.319%   $178.3998   $178.40   $178.40   $178.40  
  Purchase #2 $71.93   9.223%   $78.5641   $78.56   $78.55   $78.60  
  Purchase #3 $24.67   11.827%   $27.5877   $27.59   $27.60   $27.60  
  Purchase #4 $196.66   9.870%   $216.0703   $216.07   $216.05   $216.10  
  Purchase #5 $188.58   8.538%   $204.681   $204.68   $204.70   $204.70  
  Purchase #6 $183.85   12.404%   $206.6548   $206.65   $206.65   $206.70  
  Purchase #7 $49.32   8.234%   $53.381   $53.38   $53.40   $53.40  
  7 purchase totals = $875.27       $965.3387   $965.33   $965.35   $965.50