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 $83.78   10.721%   $92.7621   $92.76   $92.75   $92.80  
  Purchase #2 $218.93   11.695%   $244.5339   $244.53   $244.55   $244.50  
  Purchase #3 $58.78   4.328%   $61.324   $61.32   $61.30   $61.30  
  Purchase #4 $248.28   11.604%   $277.0904   $277.09   $277.10   $277.10  
  Purchase #5 $92.51   4.667%   $96.8274   $96.83   $96.85   $96.80  
  Purchase #6 $186.40   3.629%   $193.1645   $193.16   $193.15   $193.20  
  Purchase #7 $230.45   3.358%   $238.1885   $238.19   $238.20   $238.20  
  7 purchase totals = $1,119.13       $1,203.8908   $1,203.88   $1,203.90   $1,203.90