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 $135.82   5.495%   $143.2833   $143.28   $143.30   $143.30  
  Purchase #2 $190.25   3.734%   $197.3539   $197.35   $197.35   $197.40  
  Purchase #3 $53.94   8.747%   $58.6581   $58.66   $58.65   $58.70  
  Purchase #4 $139.28   10.471%   $153.864   $153.86   $153.85   $153.90  
  Purchase #5 $240.65   8.698%   $261.5817   $261.58   $261.60   $261.60  
  Purchase #6 $238.82   12.157%   $267.8533   $267.85   $267.85   $267.90  
  Purchase #7 $76.77   7.800%   $82.7581   $82.76   $82.75   $82.80  
  7 purchase totals = $1,075.53       $1,165.3524   $1,165.34   $1,165.35   $1,165.60