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 $222.96   11.493%   $248.5848   $248.58   $248.60   $248.60  
  Purchase #2 $125.95   6.789%   $134.5007   $134.50   $134.50   $134.50  
  Purchase #3 $24.31   8.193%   $26.3017   $26.30   $26.30   $26.30  
  Purchase #4 $160.35   12.606%   $180.5637   $180.56   $180.55   $180.60  
  Purchase #5 $218.46   4.322%   $227.9018   $227.90   $227.90   $227.90  
  Purchase #6 $157.90   9.166%   $172.3731   $172.37   $172.35   $172.40  
  Purchase #7 $221.71   10.505%   $245.0006   $245.00   $245.00   $245.00  
  7 purchase totals = $1,131.64       $1,235.2264   $1,235.21   $1,235.20   $1,235.30