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 $223.89   12.622%   $252.1494   $252.15   $252.15   $252.10  
  Purchase #2 $83.85   12.286%   $94.1518   $94.15   $94.15   $94.20  
  Purchase #3 $41.34   8.400%   $44.8126   $44.81   $44.80   $44.80  
  Purchase #4 $142.41   9.661%   $156.1682   $156.17   $156.15   $156.20  
  Purchase #5 $174.31   5.495%   $183.8883   $183.89   $183.90   $183.90  
  Purchase #6 $214.60   8.825%   $233.5385   $233.54   $233.55   $233.50  
  Purchase #7 $34.51   8.619%   $37.4844   $37.48   $37.50   $37.50  
  7 purchase totals = $914.91       $1,002.1932   $1,002.19   $1,002.20   $1,002.20