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 $23.38   5.522%   $24.671   $24.67   $24.65   $24.70  
  Purchase #2 $246.33   13.332%   $279.1707   $279.17   $279.15   $279.20  
  Purchase #3 $101.43   6.653%   $108.1781   $108.18   $108.20   $108.20  
  Purchase #4 $224.77   12.385%   $252.6078   $252.61   $252.60   $252.60  
  Purchase #5 $42.51   11.595%   $47.439   $47.44   $47.45   $47.40  
  Purchase #6 $136.75   9.408%   $149.6154   $149.62   $149.60   $149.60  
  Purchase #7 $5.51   9.493%   $6.0331   $6.03   $6.05   $6.00  
  7 purchase totals = $780.68       $867.7151   $867.72   $867.70   $867.70