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 $68.42   10.122%   $75.3455   $75.35   $75.35   $75.30  
  Purchase #2 $111.91   5.712%   $118.3023   $118.30   $118.30   $118.30  
  Purchase #3 $104.85   11.233%   $116.6278   $116.63   $116.65   $116.60  
  Purchase #4 $163.93   8.683%   $178.164   $178.16   $178.15   $178.20  
  Purchase #5 $105.83   8.450%   $114.7726   $114.77   $114.75   $114.80  
  Purchase #6 $243.90   7.397%   $261.9413   $261.94   $261.95   $261.90  
  Purchase #7 $187.41   12.750%   $211.3048   $211.30   $211.30   $211.30  
  7 purchase totals = $986.25       $1,076.4583   $1,076.45   $1,076.45   $1,076.40