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 $67.64   11.812%   $75.6296   $75.63   $75.65   $75.60  
  Purchase #2 $109.82   4.136%   $114.3622   $114.36   $114.35   $114.40  
  Purchase #3 $190.96   8.179%   $206.5786   $206.58   $206.60   $206.60  
  Purchase #4 $198.41   3.236%   $204.8305   $204.83   $204.85   $204.80  
  Purchase #5 $184.29   4.865%   $193.2557   $193.26   $193.25   $193.30  
  Purchase #6 $64.50   8.751%   $70.1444   $70.14   $70.15   $70.10  
  Purchase #7 $109.59   11.648%   $122.355   $122.36   $122.35   $122.40  
  7 purchase totals = $925.21       $987.1560   $987.16   $987.20   $987.20