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 $240.77   6.526%   $256.4827   $256.48   $256.50   $256.50  
  Purchase #2 $246.46   6.435%   $262.3197   $262.32   $262.30   $262.30  
  Purchase #3 $39.76   3.170%   $41.0204   $41.02   $41.00   $41.00  
  Purchase #4 $5.50   4.128%   $5.727   $5.73   $5.75   $5.70  
  Purchase #5 $91.91   12.767%   $103.6441   $103.64   $103.65   $103.60  
  Purchase #6 $174.91   6.581%   $186.4208   $186.42   $186.40   $186.40  
  Purchase #7 $154.43   12.551%   $173.8125   $173.81   $173.80   $173.80  
  7 purchase totals = $953.74       $1,029.4272   $1,029.42   $1,029.40   $1,029.30