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 $245.58   8.167%   $265.6365   $265.64   $265.65   $265.60  
  Purchase #2 $64.80   8.318%   $70.1901   $70.19   $70.20   $70.20  
  Purchase #3 $87.75   8.310%   $95.042   $95.04   $95.05   $95.00  
  Purchase #4 $146.64   5.386%   $154.538   $154.54   $154.55   $154.50  
  Purchase #5 $21.50   9.158%   $23.469   $23.47   $23.45   $23.50  
  Purchase #6 $163.68   8.326%   $177.308   $177.31   $177.30   $177.30  
  Purchase #7 $206.68   4.191%   $215.342   $215.34   $215.35   $215.30  
  7 purchase totals = $936.63       $1,001.5256   $1,001.53   $1,001.55   $1,001.40