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 $51.43   9.798%   $56.4691   $56.47   $56.45   $56.50  
  Purchase #2 $241.77   10.614%   $267.4315   $267.43   $267.45   $267.40  
  Purchase #3 $180.51   5.480%   $190.4019   $190.40   $190.40   $190.40  
  Purchase #4 $92.53   4.874%   $97.0399   $97.04   $97.05   $97.00  
  Purchase #5 $170.56   12.832%   $192.4463   $192.45   $192.45   $192.40  
  Purchase #6 $42.50   10.235%   $46.8499   $46.85   $46.85   $46.80  
  Purchase #7 $211.25   3.567%   $218.7853   $218.79   $218.80   $218.80  
  7 purchase totals = $990.55       $1,069.4239   $1,069.43   $1,069.45   $1,069.30