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 $201.45   3.274%   $208.0455   $208.05   $208.05   $208.00  
  Purchase #2 $197.83   11.856%   $221.2847   $221.28   $221.30   $221.30  
  Purchase #3 $209.29   4.407%   $218.5134   $218.51   $218.50   $218.50  
  Purchase #4 $82.72   4.572%   $86.502   $86.50   $86.50   $86.50  
  Purchase #5 $93.91   8.685%   $102.0661   $102.07   $102.05   $102.10  
  Purchase #6 $163.97   11.795%   $183.3103   $183.31   $183.30   $183.30  
  Purchase #7 $178.94   5.491%   $188.7656   $188.77   $188.75   $188.80  
  7 purchase totals = $1,128.11       $1,208.4876   $1,208.49   $1,208.45   $1,208.50