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 $92.76   12.455%   $104.3133   $104.31   $104.30   $104.30  
  Purchase #2 $223.67   13.234%   $253.2705   $253.27   $253.25   $253.30  
  Purchase #3 $152.52   7.475%   $163.9209   $163.92   $163.90   $163.90  
  Purchase #4 $248.85   6.641%   $265.3761   $265.38   $265.40   $265.40  
  Purchase #5 $250.44   5.250%   $263.5881   $263.59   $263.60   $263.60  
  Purchase #6 $24.25   13.168%   $27.4432   $27.44   $27.45   $27.40  
  Purchase #7 $145.85   11.653%   $162.8459   $162.85   $162.85   $162.80  
  7 purchase totals = $1,138.34       $1,240.7580   $1,240.76   $1,240.75   $1,240.70