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 $216.77   11.587%   $241.8871   $241.89   $241.90   $241.90  
  Purchase #2 $50.64   8.111%   $54.7474   $54.75   $54.75   $54.70  
  Purchase #3 $151.91   11.292%   $169.0637   $169.06   $169.05   $169.10  
  Purchase #4 $125.94   6.453%   $134.0669   $134.07   $134.05   $134.10  
  Purchase #5 $18.93   6.806%   $20.2184   $20.22   $20.20   $20.20  
  Purchase #6 $201.63   10.651%   $223.1056   $223.11   $223.10   $223.10  
  Purchase #7 $208.87   11.168%   $232.1966   $232.20   $232.20   $232.20  
  7 purchase totals = $974.69       $1,075.2857   $1,075.30   $1,075.25   $1,075.30