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 $96.66   3.598%   $100.1378   $100.14   $100.15   $100.10  
  Purchase #2 $209.41   10.446%   $231.285   $231.29   $231.30   $231.30  
  Purchase #3 $115.95   8.271%   $125.5402   $125.54   $125.55   $125.50  
  Purchase #4 $70.86   12.471%   $79.697   $79.70   $79.70   $79.70  
  Purchase #5 $208.91   6.763%   $223.0386   $223.04   $223.05   $223.00  
  Purchase #6 $166.45   3.795%   $172.7668   $172.77   $172.75   $172.80  
  Purchase #7 $127.65   5.530%   $134.709   $134.71   $134.70   $134.70  
  7 purchase totals = $995.89       $1,067.1744   $1,067.19   $1,067.20   $1,067.10