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 $242.65   8.214%   $262.5813   $262.58   $262.60   $262.60  
  Purchase #2 $161.29   3.172%   $166.4061   $166.41   $166.40   $166.40  
  Purchase #3 $161.84   9.412%   $177.0724   $177.07   $177.05   $177.10  
  Purchase #4 $167.77   11.405%   $186.9042   $186.90   $186.90   $186.90  
  Purchase #5 $153.39   9.822%   $168.456   $168.46   $168.45   $168.50  
  Purchase #6 $235.28   12.456%   $264.5865   $264.59   $264.60   $264.60  
  Purchase #7 $62.49   11.397%   $69.612   $69.61   $69.60   $69.60  
  7 purchase totals = $1,184.71       $1,295.6185   $1,295.62   $1,295.60   $1,295.70