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 $240.74   10.221%   $265.346   $265.35   $265.35   $265.30  
  Purchase #2 $52.57   5.766%   $55.6012   $55.60   $55.60   $55.60  
  Purchase #3 $81.70   7.775%   $88.0522   $88.05   $88.05   $88.10  
  Purchase #4 $142.77   10.513%   $157.7794   $157.78   $157.80   $157.80  
  Purchase #5 $104.79   10.644%   $115.9438   $115.94   $115.95   $115.90  
  Purchase #6 $236.93   4.685%   $248.0302   $248.03   $248.05   $248.00  
  Purchase #7 $156.92   12.674%   $176.808   $176.81   $176.80   $176.80  
  7 purchase totals = $1,016.42       $1,107.5608   $1,107.56   $1,107.60   $1,107.50