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 $151.57   10.806%   $167.9487   $167.95   $167.95   $167.90  
  Purchase #2 $184.84   11.139%   $205.4293   $205.43   $205.45   $205.40  
  Purchase #3 $157.36   3.538%   $162.9274   $162.93   $162.95   $162.90  
  Purchase #4 $44.42   12.264%   $49.8677   $49.87   $49.85   $49.90  
  Purchase #5 $164.59   3.724%   $170.7193   $170.72   $170.70   $170.70  
  Purchase #6 $158.97   8.115%   $171.8704   $171.87   $171.85   $171.90  
  Purchase #7 $74.26   9.457%   $81.2828   $81.28   $81.30   $81.30  
  7 purchase totals = $936.01       $1,010.0456   $1,010.05   $1,010.05   $1,010.00