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 $225.61   12.847%   $254.5941   $254.59   $254.60   $254.60  
  Purchase #2 $204.28   13.662%   $232.1887   $232.19   $232.20   $232.20  
  Purchase #3 $139.95   4.676%   $146.4941   $146.49   $146.50   $146.50  
  Purchase #4 $50.82   13.291%   $57.5745   $57.57   $57.55   $57.60  
  Purchase #5 $192.71   10.758%   $213.4417   $213.44   $213.45   $213.40  
  Purchase #6 $150.96   8.342%   $163.5531   $163.55   $163.55   $163.60  
  Purchase #7 $165.56   5.329%   $174.3827   $174.38   $174.40   $174.40  
  7 purchase totals = $1,129.89       $1,242.2289   $1,242.21   $1,242.25   $1,242.30