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 $200.82   10.457%   $221.8197   $221.82   $221.80   $221.80  
  Purchase #2 $17.95   5.566%   $18.9491   $18.95   $18.95   $18.90  
  Purchase #3 $204.81   12.162%   $229.719   $229.72   $229.70   $229.70  
  Purchase #4 $54.63   8.485%   $59.2654   $59.27   $59.25   $59.30  
  Purchase #5 $204.84   4.305%   $213.6584   $213.66   $213.65   $213.70  
  Purchase #6 $109.68   11.120%   $121.8764   $121.88   $121.90   $121.90  
  Purchase #7 $221.41   11.169%   $246.1393   $246.14   $246.15   $246.10  
  7 purchase totals = $1,014.14       $1,111.4273   $1,111.44   $1,111.40   $1,111.40