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 $227.54   5.346%   $239.7043   $239.70   $239.70   $239.70  
  Purchase #2 $6.75   10.578%   $7.464   $7.46   $7.45   $7.50  
  Purchase #3 $62.44   13.701%   $70.9949   $70.99   $71.00   $71.00  
  Purchase #4 $174.64   12.412%   $196.3163   $196.32   $196.30   $196.30  
  Purchase #5 $171.33   8.608%   $186.0781   $186.08   $186.10   $186.10  
  Purchase #6 $41.30   7.284%   $44.3083   $44.31   $44.30   $44.30  
  Purchase #7 $5.91   5.403%   $6.2293   $6.23   $6.25   $6.20  
  7 purchase totals = $689.91       $751.0952   $751.09   $751.10   $751.10