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 $191.39   6.357%   $203.5567   $203.56   $203.55   $203.60  
  Purchase #2 $250.91   4.370%   $261.8748   $261.87   $261.85   $261.90  
  Purchase #3 $48.80   8.658%   $53.0251   $53.03   $53.05   $53.00  
  Purchase #4 $145.69   4.434%   $152.1499   $152.15   $152.15   $152.10  
  Purchase #5 $124.36   11.597%   $138.782   $138.78   $138.80   $138.80  
  Purchase #6 $77.80   10.804%   $86.2055   $86.21   $86.20   $86.20  
  Purchase #7 $56.79   10.154%   $62.5565   $62.56   $62.55   $62.60  
  7 purchase totals = $895.74       $958.1505   $958.16   $958.15   $958.20