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 $31.96   10.826%   $35.42   $35.42   $35.40   $35.40  
  Purchase #2 $10.88   5.808%   $11.5119   $11.51   $11.50   $11.50  
  Purchase #3 $235.67   11.258%   $262.2017   $262.20   $262.20   $262.20  
  Purchase #4 $208.53   7.596%   $224.3699   $224.37   $224.35   $224.40  
  Purchase #5 $183.34   11.581%   $204.5726   $204.57   $204.55   $204.60  
  Purchase #6 $42.67   10.774%   $47.2673   $47.27   $47.25   $47.30  
  Purchase #7 $195.67   13.749%   $222.5727   $222.57   $222.55   $222.60  
  7 purchase totals = $908.72       $1,007.9161   $1,007.91   $1,007.80   $1,008.00