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 $110.56   7.681%   $119.0521   $119.05   $119.05   $119.10  
  Purchase #2 $161.91   10.358%   $178.6806   $178.68   $178.70   $178.70  
  Purchase #3 $136.40   8.714%   $148.2859   $148.29   $148.30   $148.30  
  Purchase #4 $34.55   5.595%   $36.4831   $36.48   $36.50   $36.50  
  Purchase #5 $106.93   7.852%   $115.3261   $115.33   $115.35   $115.30  
  Purchase #6 $234.91   8.837%   $255.669   $255.67   $255.65   $255.70  
  Purchase #7 $180.83   13.770%   $205.7303   $205.73   $205.75   $205.70  
  7 purchase totals = $966.09       $1,059.2271   $1,059.23   $1,059.30   $1,059.30