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 $227.89   5.536%   $240.506   $240.51   $240.50   $240.50  
  Purchase #2 $239.44   6.108%   $254.065   $254.07   $254.05   $254.10  
  Purchase #3 $102.94   8.472%   $111.6611   $111.66   $111.65   $111.70  
  Purchase #4 $226.90   13.865%   $258.3597   $258.36   $258.35   $258.40  
  Purchase #5 $109.36   7.528%   $117.5926   $117.59   $117.60   $117.60  
  Purchase #6 $106.42   10.741%   $117.8506   $117.85   $117.85   $117.90  
  Purchase #7 $187.62   3.136%   $193.5038   $193.50   $193.50   $193.50  
  7 purchase totals = $1,200.57       $1,293.5388   $1,293.54   $1,293.50   $1,293.70