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 $244.64   8.451%   $265.3145   $265.31   $265.30   $265.30  
  Purchase #2 $246.61   6.420%   $262.4424   $262.44   $262.45   $262.40  
  Purchase #3 $56.91   5.284%   $59.9171   $59.92   $59.90   $59.90  
  Purchase #4 $111.37   12.357%   $125.132   $125.13   $125.15   $125.10  
  Purchase #5 $113.62   3.547%   $117.6501   $117.65   $117.65   $117.70  
  Purchase #6 $229.41   12.340%   $257.7192   $257.72   $257.70   $257.70  
  Purchase #7 $150.76   9.797%   $165.53   $165.53   $165.55   $165.50  
  7 purchase totals = $1,153.32       $1,253.7053   $1,253.70   $1,253.70   $1,253.60