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 $61.25   4.295%   $63.8807   $63.88   $63.90   $63.90  
  Purchase #2 $48.79   13.255%   $55.2571   $55.26   $55.25   $55.30  
  Purchase #3 $33.43   4.241%   $34.8478   $34.85   $34.85   $34.80  
  Purchase #4 $19.82   13.824%   $22.5599   $22.56   $22.55   $22.60  
  Purchase #5 $66.43   10.402%   $73.34   $73.34   $73.35   $73.30  
  Purchase #6 $94.35   10.238%   $104.0096   $104.01   $104.00   $104.00  
  Purchase #7 $54.42   3.157%   $56.138   $56.14   $56.15   $56.10  
  7 purchase totals = $378.49       $410.0331   $410.04   $410.05   $410.00