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 $65.71   11.143%   $73.0321   $73.03   $73.05   $73.00  
  Purchase #2 $249.53   5.459%   $263.1518   $263.15   $263.15   $263.20  
  Purchase #3 $114.77   8.716%   $124.7734   $124.77   $124.75   $124.80  
  Purchase #4 $73.90   11.709%   $82.553   $82.55   $82.55   $82.60  
  Purchase #5 $227.58   6.113%   $241.492   $241.49   $241.50   $241.50  
  Purchase #6 $242.59   4.223%   $252.8346   $252.83   $252.85   $252.80  
  Purchase #7 $68.55   7.701%   $73.829   $73.83   $73.85   $73.80  
  7 purchase totals = $1,042.63       $1,111.6659   $1,111.65   $1,111.70   $1,111.70