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 $222.56   11.373%   $247.8717   $247.87   $247.85   $247.90  
  Purchase #2 $177.96   13.358%   $201.7319   $201.73   $201.75   $201.70  
  Purchase #3 $90.53   6.819%   $96.7032   $96.70   $96.70   $96.70  
  Purchase #4 $227.30   11.611%   $253.6918   $253.69   $253.70   $253.70  
  Purchase #5 $250.91   8.437%   $272.0793   $272.08   $272.10   $272.10  
  Purchase #6 $54.82   8.738%   $59.6102   $59.61   $59.60   $59.60  
  Purchase #7 $93.35   10.601%   $103.246   $103.25   $103.25   $103.20  
  7 purchase totals = $1,117.43       $1,234.9341   $1,234.93   $1,234.95   $1,234.90