Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.88   7.120%   $128.4155   $128.42   $128.40   $128.40  
  Purchase #2 $94.88   12.468%   $106.7096   $106.71   $106.70   $106.70  
  Purchase #3 $116.55   9.196%   $127.2679   $127.27   $127.25   $127.30  
  Purchase #4 $146.87   12.204%   $164.794   $164.79   $164.80   $164.80  
  Purchase #5 $186.68   6.330%   $198.4968   $198.50   $198.50   $198.50  
  Purchase #6 $189.83   8.347%   $205.6751   $205.68   $205.70   $205.70  
  Purchase #7 $100.74   13.375%   $114.214   $114.21   $114.20   $114.20  
  7 purchase totals = $955.43       $1,045.5729   $1,045.58   $1,045.55   $1,045.60