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 $59.41   7.841%   $64.0683   $64.07   $64.05   $64.10  
  Purchase #2 $227.75   12.683%   $256.6355   $256.64   $256.65   $256.60  
  Purchase #3 $181.79   5.628%   $192.0211   $192.02   $192.00   $192.00  
  Purchase #4 $155.40   8.259%   $168.2345   $168.23   $168.25   $168.20  
  Purchase #5 $93.38   11.647%   $104.256   $104.26   $104.25   $104.30  
  Purchase #6 $153.80   6.686%   $164.0831   $164.08   $164.10   $164.10  
  Purchase #7 $9.91   4.291%   $10.3352   $10.34   $10.35   $10.30  
  7 purchase totals = $881.44       $959.6337   $959.64   $959.65   $959.60