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 $201.27   3.428%   $208.1695   $208.17   $208.15   $208.20  
  Purchase #2 $235.91   5.772%   $249.5267   $249.53   $249.55   $249.50  
  Purchase #3 $115.91   12.425%   $130.3118   $130.31   $130.30   $130.30  
  Purchase #4 $82.47   12.564%   $92.8315   $92.83   $92.85   $92.80  
  Purchase #5 $123.34   10.713%   $136.5534   $136.55   $136.55   $136.60  
  Purchase #6 $61.32   7.388%   $65.8503   $65.85   $65.85   $65.90  
  Purchase #7 $133.75   3.337%   $138.2132   $138.21   $138.20   $138.20  
  7 purchase totals = $953.97       $1,021.4564   $1,021.45   $1,021.45   $1,021.50