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 $211.36   7.652%   $227.5333   $227.53   $227.55   $227.50  
  Purchase #2 $110.71   12.573%   $124.6296   $124.63   $124.65   $124.60  
  Purchase #3 $121.49   4.596%   $127.0737   $127.07   $127.05   $127.10  
  Purchase #4 $160.50   8.407%   $173.9932   $173.99   $174.00   $174.00  
  Purchase #5 $78.54   8.707%   $85.3785   $85.38   $85.40   $85.40  
  Purchase #6 $235.26   6.419%   $250.3613   $250.36   $250.35   $250.40  
  Purchase #7 $98.53   3.147%   $101.6307   $101.63   $101.65   $101.60  
  7 purchase totals = $1,016.39       $1,090.6003   $1,090.59   $1,090.65   $1,090.60