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 $63.47   8.135%   $68.6333   $68.63   $68.65   $68.60  
  Purchase #2 $184.75   11.119%   $205.2924   $205.29   $205.30   $205.30  
  Purchase #3 $128.48   10.238%   $141.6338   $141.63   $141.65   $141.60  
  Purchase #4 $209.51   13.613%   $238.0306   $238.03   $238.05   $238.00  
  Purchase #5 $104.47   8.247%   $113.0856   $113.09   $113.10   $113.10  
  Purchase #6 $136.36   11.498%   $152.0387   $152.04   $152.05   $152.00  
  Purchase #7 $141.83   3.575%   $146.9004   $146.90   $146.90   $146.90  
  7 purchase totals = $968.87       $1,065.6148   $1,065.61   $1,065.70   $1,065.50