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 $59.41   3.215%   $61.32   $61.32   $61.30   $61.30  
  Purchase #2 $71.87   7.427%   $77.2078   $77.21   $77.20   $77.20  
  Purchase #3 $40.73   8.499%   $44.1916   $44.19   $44.20   $44.20  
  Purchase #4 $154.76   4.621%   $161.9115   $161.91   $161.90   $161.90  
  Purchase #5 $29.68   7.416%   $31.8811   $31.88   $31.90   $31.90  
  Purchase #6 $67.91   8.684%   $73.8073   $73.81   $73.80   $73.80  
  Purchase #7 $203.62   4.291%   $212.3573   $212.36   $212.35   $212.40  
  7 purchase totals = $627.98       $662.6766   $662.68   $662.65   $662.70