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 $144.49   7.229%   $154.9352   $154.94   $154.95   $154.90  
  Purchase #2 $159.29   9.448%   $174.3397   $174.34   $174.35   $174.30  
  Purchase #3 $197.53   5.670%   $208.73   $208.73   $208.75   $208.70  
  Purchase #4 $44.83   6.446%   $47.7197   $47.72   $47.70   $47.70  
  Purchase #5 $152.26   10.595%   $168.3919   $168.39   $168.40   $168.40  
  Purchase #6 $25.86   6.717%   $27.597   $27.60   $27.60   $27.60  
  Purchase #7 $198.46   3.542%   $205.4895   $205.49   $205.50   $205.50  
  7 purchase totals = $922.72       $987.2030   $987.21   $987.25   $987.10