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 $221.44   11.457%   $246.8104   $246.81   $246.80   $246.80  
  Purchase #2 $183.40   10.523%   $202.6992   $202.70   $202.70   $202.70  
  Purchase #3 $184.92   4.798%   $193.7925   $193.79   $193.80   $193.80  
  Purchase #4 $242.30   8.519%   $262.9415   $262.94   $262.95   $262.90  
  Purchase #5 $168.59   6.806%   $180.0642   $180.06   $180.05   $180.10  
  Purchase #6 $190.72   12.440%   $214.4456   $214.45   $214.45   $214.40  
  Purchase #7 $151.25   8.249%   $163.7266   $163.73   $163.75   $163.70  
  7 purchase totals = $1,342.62       $1,464.4800   $1,464.48   $1,464.50   $1,464.40