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 $218.67   9.541%   $239.5333   $239.53   $239.55   $239.50  
  Purchase #2 $24.81   7.401%   $26.6462   $26.65   $26.65   $26.60  
  Purchase #3 $34.83   9.474%   $38.1298   $38.13   $38.15   $38.10  
  Purchase #4 $14.66   12.408%   $16.479   $16.48   $16.50   $16.50  
  Purchase #5 $198.93   11.121%   $221.053   $221.05   $221.05   $221.10  
  Purchase #6 $10.78   4.147%   $11.227   $11.23   $11.25   $11.20  
  Purchase #7 $194.89   13.533%   $221.2645   $221.26   $221.25   $221.30  
  7 purchase totals = $697.57       $774.3328   $774.33   $774.40   $774.30