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 $77.26   4.543%   $80.7699   $80.77   $80.75   $80.80  
  Purchase #2 $23.26   13.219%   $26.3347   $26.33   $26.35   $26.30  
  Purchase #3 $97.77   6.867%   $104.4839   $104.48   $104.50   $104.50  
  Purchase #4 $125.27   7.419%   $134.5638   $134.56   $134.55   $134.60  
  Purchase #5 $103.64   5.247%   $109.078   $109.08   $109.10   $109.10  
  Purchase #6 $98.38   5.789%   $104.0752   $104.08   $104.10   $104.10  
  Purchase #7 $200.58   13.377%   $227.4116   $227.41   $227.40   $227.40  
  7 purchase totals = $726.16       $786.7171   $786.71   $786.75   $786.80