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 $178.55   8.649%   $193.9928   $193.99   $194.00   $194.00  
  Purchase #2 $205.70   9.298%   $224.826   $224.83   $224.85   $224.80  
  Purchase #3 $25.34   9.207%   $27.6731   $27.67   $27.65   $27.70  
  Purchase #4 $58.45   9.751%   $64.1495   $64.15   $64.15   $64.10  
  Purchase #5 $215.28   11.143%   $239.2687   $239.27   $239.25   $239.30  
  Purchase #6 $188.32   5.288%   $198.2784   $198.28   $198.30   $198.30  
  Purchase #7 $172.66   11.845%   $193.1116   $193.11   $193.10   $193.10  
  7 purchase totals = $1,044.30       $1,141.3001   $1,141.30   $1,141.30   $1,141.30