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 $218.65   13.307%   $247.7458   $247.75   $247.75   $247.70  
  Purchase #2 $236.65   11.117%   $262.9584   $262.96   $262.95   $263.00  
  Purchase #3 $248.56   8.500%   $269.6876   $269.69   $269.70   $269.70  
  Purchase #4 $111.81   7.495%   $120.1902   $120.19   $120.20   $120.20  
  Purchase #5 $187.41   10.581%   $207.2399   $207.24   $207.25   $207.20  
  Purchase #6 $178.69   4.221%   $186.2325   $186.23   $186.25   $186.20  
  Purchase #7 $168.39   9.601%   $184.5571   $184.56   $184.55   $184.60  
  7 purchase totals = $1,350.16       $1,478.6115   $1,478.62   $1,478.65   $1,478.60