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 $115.25   3.780%   $119.6065   $119.61   $119.60   $119.60  
  Purchase #2 $88.95   3.839%   $92.3648   $92.36   $92.35   $92.40  
  Purchase #3 $210.71   8.450%   $228.515   $228.52   $228.50   $228.50  
  Purchase #4 $42.25   5.852%   $44.7225   $44.72   $44.70   $44.70  
  Purchase #5 $213.33   4.629%   $223.205   $223.21   $223.20   $223.20  
  Purchase #6 $80.31   7.801%   $86.575   $86.58   $86.60   $86.60  
  Purchase #7 $40.99   11.588%   $45.7399   $45.74   $45.75   $45.70  
  7 purchase totals = $791.79       $840.7287   $840.74   $840.70   $840.70