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 $141.36   8.660%   $153.6018   $153.60   $153.60   $153.60  
  Purchase #2 $31.95   6.871%   $34.1453   $34.15   $34.15   $34.10  
  Purchase #3 $234.41   11.524%   $261.4234   $261.42   $261.40   $261.40  
  Purchase #4 $191.79   6.190%   $203.6618   $203.66   $203.65   $203.70  
  Purchase #5 $192.66   5.104%   $202.4934   $202.49   $202.50   $202.50  
  Purchase #6 $7.79   6.435%   $8.2913   $8.29   $8.30   $8.30  
  Purchase #7 $111.26   11.193%   $123.7133   $123.71   $123.70   $123.70  
  7 purchase totals = $911.22       $987.3303   $987.32   $987.30   $987.30