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 $60.41   11.302%   $67.2375   $67.24   $67.25   $67.20  
  Purchase #2 $151.79   5.526%   $160.1779   $160.18   $160.20   $160.20  
  Purchase #3 $146.49   3.572%   $151.7226   $151.72   $151.70   $151.70  
  Purchase #4 $215.62   11.443%   $240.2934   $240.29   $240.30   $240.30  
  Purchase #5 $121.91   7.787%   $131.4031   $131.40   $131.40   $131.40  
  Purchase #6 $214.42   13.792%   $243.9928   $243.99   $244.00   $244.00  
  Purchase #7 $239.84   8.678%   $260.6533   $260.65   $260.65   $260.70  
  7 purchase totals = $1,150.48       $1,255.4806   $1,255.47   $1,255.50   $1,255.50