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 $26.48   11.842%   $29.6158   $29.62   $29.60   $29.60  
  Purchase #2 $207.27   8.810%   $225.5305   $225.53   $225.55   $225.50  
  Purchase #3 $27.36   12.497%   $30.7792   $30.78   $30.80   $30.80  
  Purchase #4 $196.57   13.788%   $223.6731   $223.67   $223.65   $223.70  
  Purchase #5 $113.57   12.745%   $128.0445   $128.04   $128.05   $128.00  
  Purchase #6 $157.36   13.701%   $178.9199   $178.92   $178.90   $178.90  
  Purchase #7 $230.55   7.686%   $248.2701   $248.27   $248.25   $248.30  
  7 purchase totals = $959.16       $1,064.8331   $1,064.83   $1,064.80   $1,064.80