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 $57.93   6.813%   $61.8768   $61.88   $61.90   $61.90  
  Purchase #2 $219.58   4.158%   $228.7101   $228.71   $228.70   $228.70  
  Purchase #3 $172.76   10.312%   $190.575   $190.58   $190.60   $190.60  
  Purchase #4 $117.70   12.619%   $132.5526   $132.55   $132.55   $132.60  
  Purchase #5 $193.35   5.274%   $203.5473   $203.55   $203.55   $203.50  
  Purchase #6 $79.37   5.853%   $84.0155   $84.02   $84.00   $84.00  
  Purchase #7 $113.53   10.452%   $125.3962   $125.40   $125.40   $125.40  
  7 purchase totals = $954.22       $1,026.6735   $1,026.69   $1,026.70   $1,026.70