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 $208.27   3.229%   $214.995   $215.00   $215.00   $215.00  
  Purchase #2 $180.39   11.408%   $200.9689   $200.97   $200.95   $201.00  
  Purchase #3 $132.32   5.498%   $139.595   $139.60   $139.60   $139.60  
  Purchase #4 $181.31   10.136%   $199.6876   $199.69   $199.70   $199.70  
  Purchase #5 $152.36   9.693%   $167.1283   $167.13   $167.15   $167.10  
  Purchase #6 $237.92   10.732%   $263.4536   $263.45   $263.45   $263.50  
  Purchase #7 $185.49   4.535%   $193.902   $193.90   $193.90   $193.90  
  7 purchase totals = $1,278.06       $1,379.7304   $1,379.74   $1,379.75   $1,379.80