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 $214.58   11.189%   $238.5894   $238.59   $238.60   $238.60  
  Purchase #2 $162.76   9.712%   $178.5673   $178.57   $178.55   $178.60  
  Purchase #3 $5.55   12.466%   $6.2419   $6.24   $6.25   $6.20  
  Purchase #4 $192.38   12.749%   $216.9065   $216.91   $216.90   $216.90  
  Purchase #5 $79.63   8.359%   $86.2863   $86.29   $86.30   $86.30  
  Purchase #6 $147.72   5.347%   $155.6186   $155.62   $155.60   $155.60  
  Purchase #7 $66.95   6.804%   $71.5053   $71.51   $71.50   $71.50  
  7 purchase totals = $869.57       $953.7153   $953.73   $953.70   $953.70