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 $233.63   13.273%   $264.6397   $264.64   $264.65   $264.60  
  Purchase #2 $158.65   11.275%   $176.5378   $176.54   $176.55   $176.50  
  Purchase #3 $30.41   7.472%   $32.6822   $32.68   $32.70   $32.70  
  Purchase #4 $194.33   6.182%   $206.3435   $206.34   $206.35   $206.30  
  Purchase #5 $123.76   5.828%   $130.9727   $130.97   $130.95   $131.00  
  Purchase #6 $187.54   10.389%   $207.0235   $207.02   $207.00   $207.00  
  Purchase #7 $36.58   3.521%   $37.868   $37.87   $37.85   $37.90  
  7 purchase totals = $964.90       $1,056.0674   $1,056.06   $1,056.05   $1,056.00