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 $244.86   3.407%   $253.2024   $253.20   $253.20   $253.20  
  Purchase #2 $239.55   5.721%   $253.2547   $253.25   $253.25   $253.30  
  Purchase #3 $234.31   13.670%   $266.3402   $266.34   $266.35   $266.30  
  Purchase #4 $108.84   9.512%   $119.1929   $119.19   $119.20   $119.20  
  Purchase #5 $117.99   6.863%   $126.0877   $126.09   $126.10   $126.10  
  Purchase #6 $48.36   6.215%   $51.3656   $51.37   $51.35   $51.40  
  Purchase #7 $113.93   8.505%   $123.6197   $123.62   $123.60   $123.60  
  7 purchase totals = $1,107.84       $1,193.0632   $1,193.06   $1,193.05   $1,193.10