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 $95.56   11.704%   $106.7443   $106.74   $106.75   $106.70  
  Purchase #2 $16.33   12.140%   $18.3125   $18.31   $18.30   $18.30  
  Purchase #3 $106.53   7.377%   $114.3887   $114.39   $114.40   $114.40  
  Purchase #4 $161.86   3.571%   $167.64   $167.64   $167.65   $167.60  
  Purchase #5 $236.54   9.656%   $259.3803   $259.38   $259.40   $259.40  
  Purchase #6 $222.42   12.304%   $249.7866   $249.79   $249.80   $249.80  
  Purchase #7 $163.25   12.219%   $183.1975   $183.20   $183.20   $183.20  
  7 purchase totals = $1,002.49       $1,099.4499   $1,099.45   $1,099.50   $1,099.40