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 $61.84   8.482%   $67.0853   $67.09   $67.10   $67.10  
  Purchase #2 $243.86   8.112%   $263.6419   $263.64   $263.65   $263.60  
  Purchase #3 $224.77   10.590%   $248.5731   $248.57   $248.55   $248.60  
  Purchase #4 $7.75   7.457%   $8.3279   $8.33   $8.35   $8.30  
  Purchase #5 $196.78   9.507%   $215.4879   $215.49   $215.50   $215.50  
  Purchase #6 $88.81   8.652%   $96.4938   $96.49   $96.50   $96.50  
  Purchase #7 $51.39   9.118%   $56.0757   $56.08   $56.10   $56.10  
  7 purchase totals = $875.20       $955.6856   $955.69   $955.75   $955.70