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 $156.25   4.557%   $163.3703   $163.37   $163.35   $163.40  
  Purchase #2 $143.71   4.459%   $150.118   $150.12   $150.10   $150.10  
  Purchase #3 $114.60   7.122%   $122.7618   $122.76   $122.75   $122.80  
  Purchase #4 $18.35   10.498%   $20.2764   $20.28   $20.30   $20.30  
  Purchase #5 $161.83   7.273%   $173.5999   $173.60   $173.60   $173.60  
  Purchase #6 $105.81   8.290%   $114.5816   $114.58   $114.60   $114.60  
  Purchase #7 $131.66   10.424%   $145.3842   $145.38   $145.40   $145.40  
  7 purchase totals = $832.21       $890.0922   $890.09   $890.10   $890.20