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 $203.63   5.223%   $214.2656   $214.27   $214.25   $214.30  
  Purchase #2 $44.56   5.794%   $47.1418   $47.14   $47.15   $47.10  
  Purchase #3 $183.65   10.354%   $202.6651   $202.67   $202.65   $202.70  
  Purchase #4 $156.29   13.641%   $177.6095   $177.61   $177.60   $177.60  
  Purchase #5 $25.97   4.758%   $27.2057   $27.21   $27.20   $27.20  
  Purchase #6 $74.93   7.553%   $80.5895   $80.59   $80.60   $80.60  
  Purchase #7 $250.27   7.452%   $268.9201   $268.92   $268.90   $268.90  
  7 purchase totals = $939.30       $1,018.3973   $1,018.41   $1,018.35   $1,018.40