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 $95.91   10.150%   $105.6449   $105.64   $105.65   $105.60  
  Purchase #2 $245.76   5.569%   $259.4464   $259.45   $259.45   $259.40  
  Purchase #3 $152.93   4.172%   $159.3102   $159.31   $159.30   $159.30  
  Purchase #4 $201.65   3.125%   $207.9516   $207.95   $207.95   $208.00  
  Purchase #5 $202.37   13.223%   $229.1294   $229.13   $229.15   $229.10  
  Purchase #6 $246.40   10.556%   $272.41   $272.41   $272.40   $272.40  
  Purchase #7 $53.40   12.247%   $59.9399   $59.94   $59.95   $59.90  
  7 purchase totals = $1,198.42       $1,293.8324   $1,293.83   $1,293.85   $1,293.70