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 $247.73   5.438%   $261.2016   $261.20   $261.20   $261.20  
  Purchase #2 $114.54   5.168%   $120.4594   $120.46   $120.45   $120.50  
  Purchase #3 $46.54   6.483%   $49.5572   $49.56   $49.55   $49.60  
  Purchase #4 $36.34   4.438%   $37.9528   $37.95   $37.95   $38.00  
  Purchase #5 $195.99   3.160%   $202.1833   $202.18   $202.20   $202.20  
  Purchase #6 $30.28   5.832%   $32.0459   $32.05   $32.05   $32.00  
  Purchase #7 $127.48   4.634%   $133.3874   $133.39   $133.40   $133.40  
  7 purchase totals = $798.90       $836.7876   $836.79   $836.80   $836.90