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 $56.96   3.353%   $58.8699   $58.87   $58.85   $58.90  
  Purchase #2 $53.52   13.828%   $60.9207   $60.92   $60.90   $60.90  
  Purchase #3 $248.54   5.305%   $261.725   $261.73   $261.75   $261.70  
  Purchase #4 $126.83   8.834%   $138.0342   $138.03   $138.05   $138.00  
  Purchase #5 $235.54   3.706%   $244.2691   $244.27   $244.25   $244.30  
  Purchase #6 $210.69   5.390%   $222.0462   $222.05   $222.05   $222.00  
  Purchase #7 $202.69   9.535%   $222.0165   $222.02   $222.00   $222.00  
  7 purchase totals = $1,134.77       $1,207.8816   $1,207.89   $1,207.85   $1,207.80