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 $67.70   5.272%   $71.2691   $71.27   $71.25   $71.30  
  Purchase #2 $124.49   9.854%   $136.7572   $136.76   $136.75   $136.80  
  Purchase #3 $239.29   7.748%   $257.8302   $257.83   $257.85   $257.80  
  Purchase #4 $108.27   8.728%   $117.7198   $117.72   $117.70   $117.70  
  Purchase #5 $226.51   10.559%   $250.4272   $250.43   $250.45   $250.40  
  Purchase #6 $21.36   12.874%   $24.1099   $24.11   $24.10   $24.10  
  Purchase #7 $188.83   7.723%   $203.4133   $203.41   $203.40   $203.40  
  7 purchase totals = $976.45       $1,061.5267   $1,061.53   $1,061.50   $1,061.50