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 $201.84   12.552%   $227.175   $227.18   $227.20   $227.20  
  Purchase #2 $162.34   12.448%   $182.5481   $182.55   $182.55   $182.50  
  Purchase #3 $99.69   8.386%   $108.05   $108.05   $108.05   $108.10  
  Purchase #4 $219.88   12.550%   $247.4749   $247.47   $247.45   $247.50  
  Purchase #5 $6.35   4.623%   $6.6436   $6.64   $6.65   $6.60  
  Purchase #6 $52.62   5.298%   $55.4078   $55.41   $55.40   $55.40  
  Purchase #7 $180.45   6.543%   $192.2568   $192.26   $192.25   $192.30  
  7 purchase totals = $923.17       $1,019.5562   $1,019.56   $1,019.55   $1,019.60