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 $218.35   8.525%   $236.9643   $236.96   $236.95   $237.00  
  Purchase #2 $233.37   6.641%   $248.8681   $248.87   $248.85   $248.90  
  Purchase #3 $62.69   8.409%   $67.9616   $67.96   $67.95   $68.00  
  Purchase #4 $240.96   7.479%   $258.9814   $258.98   $259.00   $259.00  
  Purchase #5 $47.93   6.720%   $51.1509   $51.15   $51.15   $51.20  
  Purchase #6 $45.87   11.455%   $51.1244   $51.12   $51.10   $51.10  
  Purchase #7 $197.26   8.864%   $214.7451   $214.75   $214.75   $214.70  
  7 purchase totals = $1,046.43       $1,129.7958   $1,129.79   $1,129.75   $1,129.90