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 $29.65   12.211%   $33.2706   $33.27   $33.25   $33.30  
  Purchase #2 $192.59   5.476%   $203.1362   $203.14   $203.15   $203.10  
  Purchase #3 $67.70   8.145%   $73.2142   $73.21   $73.20   $73.20  
  Purchase #4 $208.71   4.681%   $218.4797   $218.48   $218.50   $218.50  
  Purchase #5 $234.32   7.807%   $252.6134   $252.61   $252.60   $252.60  
  Purchase #6 $211.95   4.241%   $220.9388   $220.94   $220.95   $220.90  
  Purchase #7 $6.79   12.413%   $7.6328   $7.63   $7.65   $7.60  
  7 purchase totals = $951.71       $1,009.2857   $1,009.28   $1,009.30   $1,009.20