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 $91.58   13.117%   $103.5925   $103.59   $103.60   $103.60  
  Purchase #2 $190.57   9.185%   $208.0739   $208.07   $208.05   $208.10  
  Purchase #3 $173.75   13.817%   $197.757   $197.76   $197.75   $197.80  
  Purchase #4 $38.85   11.291%   $43.2366   $43.24   $43.25   $43.20  
  Purchase #5 $136.71   13.390%   $155.0155   $155.02   $155.00   $155.00  
  Purchase #6 $205.45   9.253%   $224.4603   $224.46   $224.45   $224.50  
  Purchase #7 $241.91   12.423%   $271.9625   $271.96   $271.95   $272.00  
  7 purchase totals = $1,078.82       $1,204.0983   $1,204.10   $1,204.05   $1,204.20