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 $231.85   13.233%   $262.5307   $262.53   $262.55   $262.50  
  Purchase #2 $134.35   9.141%   $146.6309   $146.63   $146.65   $146.60  
  Purchase #3 $248.66   9.670%   $272.7054   $272.71   $272.70   $272.70  
  Purchase #4 $155.52   5.582%   $164.2011   $164.20   $164.20   $164.20  
  Purchase #5 $213.29   10.592%   $235.8817   $235.88   $235.90   $235.90  
  Purchase #6 $16.93   5.407%   $17.8454   $17.85   $17.85   $17.80  
  Purchase #7 $38.30   3.856%   $39.7768   $39.78   $39.80   $39.80  
  7 purchase totals = $1,038.90       $1,139.5720   $1,139.58   $1,139.65   $1,139.50