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 $202.51   12.402%   $227.6253   $227.63   $227.65   $227.60  
  Purchase #2 $218.51   9.565%   $239.4105   $239.41   $239.40   $239.40  
  Purchase #3 $145.91   13.493%   $165.5976   $165.60   $165.60   $165.60  
  Purchase #4 $117.68   5.585%   $124.2524   $124.25   $124.25   $124.30  
  Purchase #5 $158.93   11.627%   $177.4088   $177.41   $177.40   $177.40  
  Purchase #6 $48.57   13.679%   $55.2139   $55.21   $55.20   $55.20  
  Purchase #7 $40.38   9.234%   $44.1087   $44.11   $44.10   $44.10  
  7 purchase totals = $932.49       $1,033.6172   $1,033.62   $1,033.60   $1,033.60