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 $59.81   13.179%   $67.6924   $67.69   $67.70   $67.70  
  Purchase #2 $230.93   11.515%   $257.5216   $257.52   $257.50   $257.50  
  Purchase #3 $102.35   4.794%   $107.2567   $107.26   $107.25   $107.30  
  Purchase #4 $182.36   7.701%   $196.4035   $196.40   $196.40   $196.40  
  Purchase #5 $17.39   5.770%   $18.3934   $18.39   $18.40   $18.40  
  Purchase #6 $6.64   6.626%   $7.08   $7.08   $7.10   $7.10  
  Purchase #7 $248.96   8.590%   $270.3457   $270.35   $270.35   $270.30  
  7 purchase totals = $848.44       $924.6933   $924.69   $924.70   $924.70