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 $186.58   4.327%   $194.6533   $194.65   $194.65   $194.70  
  Purchase #2 $12.42   9.220%   $13.5651   $13.57   $13.55   $13.60  
  Purchase #3 $32.48   3.672%   $33.6727   $33.67   $33.65   $33.70  
  Purchase #4 $66.77   11.187%   $74.2396   $74.24   $74.25   $74.20  
  Purchase #5 $166.91   6.833%   $178.315   $178.32   $178.30   $178.30  
  Purchase #6 $101.83   12.535%   $114.5944   $114.59   $114.60   $114.60  
  Purchase #7 $68.53   7.806%   $73.8795   $73.88   $73.90   $73.90  
  7 purchase totals = $635.52       $682.9196   $682.92   $682.90   $683.00