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 $46.94   7.293%   $50.3633   $50.36   $50.35   $50.40  
  Purchase #2 $232.54   12.612%   $261.8679   $261.87   $261.85   $261.90  
  Purchase #3 $26.91   8.274%   $29.1365   $29.14   $29.15   $29.10  
  Purchase #4 $81.46   11.436%   $90.7758   $90.78   $90.80   $90.80  
  Purchase #5 $216.31   13.567%   $245.6568   $245.66   $245.65   $245.70  
  Purchase #6 $214.83   5.623%   $226.9099   $226.91   $226.90   $226.90  
  Purchase #7 $226.26   12.278%   $254.0402   $254.04   $254.05   $254.00  
  7 purchase totals = $1,045.25       $1,158.7504   $1,158.76   $1,158.75   $1,158.80