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 $56.83   9.571%   $62.2692   $62.27   $62.25   $62.30  
  Purchase #2 $41.67   13.591%   $47.3334   $47.33   $47.35   $47.30  
  Purchase #3 $184.50   3.406%   $190.7841   $190.78   $190.80   $190.80  
  Purchase #4 $70.25   6.525%   $74.8338   $74.83   $74.85   $74.80  
  Purchase #5 $191.98   11.822%   $214.6759   $214.68   $214.70   $214.70  
  Purchase #6 $77.40   6.602%   $82.5099   $82.51   $82.50   $82.50  
  Purchase #7 $212.76   11.332%   $236.87   $236.87   $236.85   $236.90  
  7 purchase totals = $835.39       $909.2763   $909.27   $909.30   $909.30