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 $179.87   8.379%   $194.9413   $194.94   $194.95   $194.90  
  Purchase #2 $127.75   6.729%   $136.3463   $136.35   $136.35   $136.30  
  Purchase #3 $220.35   6.425%   $234.5075   $234.51   $234.50   $234.50  
  Purchase #4 $151.35   6.714%   $161.5116   $161.51   $161.50   $161.50  
  Purchase #5 $82.43   5.208%   $86.723   $86.72   $86.70   $86.70  
  Purchase #6 $164.91   10.610%   $182.407   $182.41   $182.40   $182.40  
  Purchase #7 $116.81   4.113%   $121.6144   $121.61   $121.60   $121.60  
  7 purchase totals = $1,043.47       $1,118.0511   $1,118.05   $1,118.00   $1,117.90