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 $54.99   10.633%   $60.8371   $60.84   $60.85   $60.80  
  Purchase #2 $180.85   11.790%   $202.1722   $202.17   $202.15   $202.20  
  Purchase #3 $15.28   13.148%   $17.289   $17.29   $17.30   $17.30  
  Purchase #4 $117.60   11.147%   $130.7089   $130.71   $130.70   $130.70  
  Purchase #5 $242.87   8.103%   $262.5498   $262.55   $262.55   $262.50  
  Purchase #6 $105.47   7.362%   $113.2347   $113.23   $113.25   $113.20  
  Purchase #7 $154.40   11.522%   $172.19   $172.19   $172.20   $172.20  
  7 purchase totals = $871.46       $958.9817   $958.98   $959.00   $958.90