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 $86.45   13.583%   $98.1925   $98.19   $98.20   $98.20  
  Purchase #2 $116.35   5.241%   $122.4479   $122.45   $122.45   $122.40  
  Purchase #3 $190.39   8.127%   $205.863   $205.86   $205.85   $205.90  
  Purchase #4 $190.93   3.713%   $198.0192   $198.02   $198.00   $198.00  
  Purchase #5 $146.92   5.215%   $154.5819   $154.58   $154.60   $154.60  
  Purchase #6 $154.64   12.192%   $173.4937   $173.49   $173.50   $173.50  
  Purchase #7 $185.87   6.434%   $197.8289   $197.83   $197.85   $197.80  
  7 purchase totals = $1,071.55       $1,150.4271   $1,150.42   $1,150.45   $1,150.40