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 $49.69   9.187%   $54.255   $54.26   $54.25   $54.30  
  Purchase #2 $208.73   13.391%   $236.681   $236.68   $236.70   $236.70  
  Purchase #3 $223.79   10.464%   $247.2074   $247.21   $247.20   $247.20  
  Purchase #4 $94.78   10.587%   $104.8144   $104.81   $104.80   $104.80  
  Purchase #5 $63.89   5.477%   $67.3893   $67.39   $67.40   $67.40  
  Purchase #6 $22.37   4.543%   $23.3863   $23.39   $23.40   $23.40  
  Purchase #7 $39.26   11.106%   $43.6202   $43.62   $43.60   $43.60  
  7 purchase totals = $702.51       $777.3536   $777.36   $777.35   $777.40