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 $236.70   7.306%   $253.9933   $253.99   $254.00   $254.00  
  Purchase #2 $109.95   8.397%   $119.1825   $119.18   $119.20   $119.20  
  Purchase #3 $23.70   10.732%   $26.2435   $26.24   $26.25   $26.20  
  Purchase #4 $247.95   7.156%   $265.6933   $265.69   $265.70   $265.70  
  Purchase #5 $34.72   8.200%   $37.567   $37.57   $37.55   $37.60  
  Purchase #6 $185.85   11.710%   $207.613   $207.61   $207.60   $207.60  
  Purchase #7 $230.71   9.350%   $252.2814   $252.28   $252.30   $252.30  
  7 purchase totals = $1,069.58       $1,162.5740   $1,162.56   $1,162.60   $1,162.60