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 $67.30   3.311%   $69.5283   $69.53   $69.55   $69.50  
  Purchase #2 $9.89   7.667%   $10.6483   $10.65   $10.65   $10.60  
  Purchase #3 $151.79   6.456%   $161.5896   $161.59   $161.60   $161.60  
  Purchase #4 $230.97   9.393%   $252.665   $252.67   $252.65   $252.70  
  Purchase #5 $112.98   7.783%   $121.7732   $121.77   $121.75   $121.80  
  Purchase #6 $213.92   8.685%   $232.499   $232.50   $232.50   $232.50  
  Purchase #7 $248.53   12.143%   $278.709   $278.71   $278.70   $278.70  
  7 purchase totals = $1,035.38       $1,127.4124   $1,127.42   $1,127.40   $1,127.40