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 $232.58   13.475%   $263.9202   $263.92   $263.90   $263.90  
  Purchase #2 $56.25   6.647%   $59.9889   $59.99   $60.00   $60.00  
  Purchase #3 $152.70   7.523%   $164.1876   $164.19   $164.20   $164.20  
  Purchase #4 $168.40   11.619%   $187.9664   $187.97   $187.95   $188.00  
  Purchase #5 $121.25   6.751%   $129.4356   $129.44   $129.45   $129.40  
  Purchase #6 $232.86   4.141%   $242.5027   $242.50   $242.50   $242.50  
  Purchase #7 $121.77   11.130%   $135.323   $135.32   $135.30   $135.30  
  7 purchase totals = $1,085.81       $1,183.3244   $1,183.33   $1,183.30   $1,183.30