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 $59.31   9.632%   $65.0227   $65.02   $65.00   $65.00  
  Purchase #2 $230.38   9.439%   $252.1256   $252.13   $252.15   $252.10  
  Purchase #3 $86.64   12.146%   $97.1633   $97.16   $97.15   $97.20  
  Purchase #4 $162.68   8.450%   $176.4265   $176.43   $176.45   $176.40  
  Purchase #5 $90.29   6.863%   $96.4866   $96.49   $96.50   $96.50  
  Purchase #6 $61.45   4.251%   $64.0622   $64.06   $64.05   $64.10  
  Purchase #7 $202.30   3.237%   $208.8485   $208.85   $208.85   $208.80  
  7 purchase totals = $893.05       $960.1354   $960.14   $960.15   $960.10