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 $42.33   11.824%   $47.3351   $47.34   $47.35   $47.30  
  Purchase #2 $118.44   10.558%   $130.9449   $130.94   $130.95   $130.90  
  Purchase #3 $161.59   9.509%   $176.9556   $176.96   $176.95   $177.00  
  Purchase #4 $96.29   8.713%   $104.6797   $104.68   $104.70   $104.70  
  Purchase #5 $190.88   10.108%   $210.1742   $210.17   $210.15   $210.20  
  Purchase #6 $77.97   5.477%   $82.2404   $82.24   $82.25   $82.20  
  Purchase #7 $241.83   9.873%   $265.7059   $265.71   $265.70   $265.70  
  7 purchase totals = $929.33       $1,018.0358   $1,018.04   $1,018.05   $1,018.00