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 $86.39   12.135%   $96.8734   $96.87   $96.85   $96.90  
  Purchase #2 $227.26   11.216%   $252.7495   $252.75   $252.75   $252.70  
  Purchase #3 $116.62   6.738%   $124.4779   $124.48   $124.50   $124.50  
  Purchase #4 $238.31   3.806%   $247.3801   $247.38   $247.40   $247.40  
  Purchase #5 $176.66   8.793%   $192.1937   $192.19   $192.20   $192.20  
  Purchase #6 $84.87   3.565%   $87.8956   $87.90   $87.90   $87.90  
  Purchase #7 $16.82   12.605%   $18.9402   $18.94   $18.95   $18.90  
  7 purchase totals = $946.93       $1,020.5104   $1,020.51   $1,020.55   $1,020.50