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 $53.86   5.802%   $56.985   $56.99   $57.00   $57.00  
  Purchase #2 $152.38   5.709%   $161.0794   $161.08   $161.10   $161.10  
  Purchase #3 $111.81   12.469%   $125.7516   $125.75   $125.75   $125.80  
  Purchase #4 $250.61   13.493%   $284.4248   $284.42   $284.40   $284.40  
  Purchase #5 $239.66   7.302%   $257.16   $257.16   $257.15   $257.20  
  Purchase #6 $115.72   13.341%   $131.1582   $131.16   $131.15   $131.20  
  Purchase #7 $233.77   5.545%   $246.7325   $246.73   $246.75   $246.70  
  7 purchase totals = $1,157.81       $1,263.2915   $1,263.29   $1,263.30   $1,263.40