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 $96.39   9.839%   $105.8738   $105.87   $105.85   $105.90  
  Purchase #2 $73.35   5.637%   $77.4847   $77.48   $77.50   $77.50  
  Purchase #3 $238.33   11.783%   $266.4124   $266.41   $266.40   $266.40  
  Purchase #4 $236.53   7.794%   $254.9651   $254.97   $254.95   $255.00  
  Purchase #5 $214.76   4.568%   $224.5702   $224.57   $224.55   $224.60  
  Purchase #6 $217.78   9.244%   $237.9116   $237.91   $237.90   $237.90  
  Purchase #7 $161.67   9.414%   $176.8896   $176.89   $176.90   $176.90  
  7 purchase totals = $1,238.81       $1,344.1074   $1,344.10   $1,344.05   $1,344.20