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 $235.61   11.348%   $262.347   $262.35   $262.35   $262.30  
  Purchase #2 $84.80   9.655%   $92.9874   $92.99   $93.00   $93.00  
  Purchase #3 $221.29   5.497%   $233.4543   $233.45   $233.45   $233.50  
  Purchase #4 $174.39   13.405%   $197.767   $197.77   $197.75   $197.80  
  Purchase #5 $227.53   11.256%   $253.1408   $253.14   $253.15   $253.10  
  Purchase #6 $58.81   12.532%   $66.1801   $66.18   $66.20   $66.20  
  Purchase #7 $214.81   7.358%   $230.6157   $230.62   $230.60   $230.60  
  7 purchase totals = $1,217.24       $1,336.4923   $1,336.50   $1,336.50   $1,336.50