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 $232.46   6.685%   $248   $248.00   $248.00   $248.00  
  Purchase #2 $245.67   4.420%   $256.5286   $256.53   $256.55   $256.50  
  Purchase #3 $248.63   3.375%   $257.0213   $257.02   $257.00   $257.00  
  Purchase #4 $84.36   11.180%   $93.7914   $93.79   $93.80   $93.80  
  Purchase #5 $217.74   9.122%   $237.6022   $237.60   $237.60   $237.60  
  Purchase #6 $146.76   3.814%   $152.3574   $152.36   $152.35   $152.40  
  Purchase #7 $101.99   13.445%   $115.7026   $115.70   $115.70   $115.70  
  7 purchase totals = $1,277.61       $1,361.0035   $1,361.00   $1,361.00   $1,361.00