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 $213.34   10.715%   $236.1994   $236.20   $236.20   $236.20  
  Purchase #2 $168.49   5.818%   $178.2927   $178.29   $178.30   $178.30  
  Purchase #3 $26.90   10.538%   $29.7347   $29.73   $29.75   $29.70  
  Purchase #4 $180.38   5.476%   $190.2576   $190.26   $190.25   $190.30  
  Purchase #5 $113.95   5.479%   $120.1933   $120.19   $120.20   $120.20  
  Purchase #6 $166.26   12.359%   $186.8081   $186.81   $186.80   $186.80  
  Purchase #7 $159.59   10.783%   $176.7986   $176.80   $176.80   $176.80  
  7 purchase totals = $1,028.91       $1,118.2844   $1,118.28   $1,118.30   $1,118.30