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 $33.96   7.787%   $36.6045   $36.60   $36.60   $36.60  
  Purchase #2 $207.49   5.537%   $218.9787   $218.98   $219.00   $219.00  
  Purchase #3 $179.29   13.202%   $202.9599   $202.96   $202.95   $203.00  
  Purchase #4 $237.87   4.577%   $248.7573   $248.76   $248.75   $248.80  
  Purchase #5 $144.70   9.748%   $158.8054   $158.81   $158.80   $158.80  
  Purchase #6 $233.93   8.161%   $253.021   $253.02   $253.00   $253.00  
  Purchase #7 $236.85   3.576%   $245.3198   $245.32   $245.30   $245.30  
  7 purchase totals = $1,274.09       $1,364.4466   $1,364.45   $1,364.40   $1,364.50