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 $208.68   11.374%   $232.4153   $232.42   $232.40   $232.40  
  Purchase #2 $231.62   4.240%   $241.4407   $241.44   $241.45   $241.40  
  Purchase #3 $151.86   8.691%   $165.0582   $165.06   $165.05   $165.10  
  Purchase #4 $192.85   3.874%   $200.321   $200.32   $200.30   $200.30  
  Purchase #5 $124.78   13.522%   $141.6528   $141.65   $141.65   $141.70  
  Purchase #6 $140.31   11.762%   $156.8133   $156.81   $156.80   $156.80  
  Purchase #7 $202.44   10.705%   $224.1112   $224.11   $224.10   $224.10  
  7 purchase totals = $1,252.54       $1,361.8125   $1,361.81   $1,361.75   $1,361.80