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 $226.90   10.201%   $250.0461   $250.05   $250.05   $250.00  
  Purchase #2 $153.92   3.451%   $159.2318   $159.23   $159.25   $159.20  
  Purchase #3 $87.32   10.393%   $96.3952   $96.40   $96.40   $96.40  
  Purchase #4 $179.93   12.352%   $202.155   $202.16   $202.15   $202.20  
  Purchase #5 $192.87   11.484%   $215.0192   $215.02   $215.00   $215.00  
  Purchase #6 $39.28   13.862%   $44.725   $44.73   $44.75   $44.70  
  Purchase #7 $224.28   7.398%   $240.8722   $240.87   $240.85   $240.90  
  7 purchase totals = $1,104.50       $1,208.4445   $1,208.46   $1,208.45   $1,208.40