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 $227.77   6.138%   $241.7505   $241.75   $241.75   $241.80  
  Purchase #2 $166.57   6.397%   $177.2255   $177.23   $177.25   $177.20  
  Purchase #3 $84.93   13.775%   $96.6291   $96.63   $96.65   $96.60  
  Purchase #4 $110.97   3.461%   $114.8107   $114.81   $114.80   $114.80  
  Purchase #5 $214.77   7.752%   $231.419   $231.42   $231.40   $231.40  
  Purchase #6 $125.58   10.155%   $138.3326   $138.33   $138.35   $138.30  
  Purchase #7 $150.84   10.537%   $166.734   $166.73   $166.75   $166.70  
  7 purchase totals = $1,081.43       $1,166.9014   $1,166.90   $1,166.95   $1,166.80