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 $122.68   9.516%   $134.3542   $134.35   $134.35   $134.40  
  Purchase #2 $8.32   6.256%   $8.8405   $8.84   $8.85   $8.80  
  Purchase #3 $68.54   9.557%   $75.0904   $75.09   $75.10   $75.10  
  Purchase #4 $115.92   10.157%   $127.694   $127.69   $127.70   $127.70  
  Purchase #5 $208.90   6.178%   $221.8058   $221.81   $221.80   $221.80  
  Purchase #6 $191.93   3.340%   $198.3405   $198.34   $198.35   $198.30  
  Purchase #7 $248.37   8.144%   $268.5973   $268.60   $268.60   $268.60  
  7 purchase totals = $964.66       $1,034.7227   $1,034.72   $1,034.75   $1,034.70