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 $237.28   11.211%   $263.8815   $263.88   $263.90   $263.90  
  Purchase #2 $130.36   12.159%   $146.2105   $146.21   $146.20   $146.20  
  Purchase #3 $109.25   4.820%   $114.5159   $114.52   $114.50   $114.50  
  Purchase #4 $159.81   10.345%   $176.3423   $176.34   $176.35   $176.30  
  Purchase #5 $163.34   7.459%   $175.5235   $175.52   $175.50   $175.50  
  Purchase #6 $13.74   4.224%   $14.3204   $14.32   $14.30   $14.30  
  Purchase #7 $91.64   11.615%   $102.284   $102.28   $102.30   $102.30  
  7 purchase totals = $905.42       $993.0781   $993.07   $993.05   $993.00