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 $157.67   8.629%   $171.2753   $171.28   $171.30   $171.30  
  Purchase #2 $214.40   11.580%   $239.2275   $239.23   $239.25   $239.20  
  Purchase #3 $177.91   5.422%   $187.5563   $187.56   $187.55   $187.60  
  Purchase #4 $88.83   5.723%   $93.9137   $93.91   $93.90   $93.90  
  Purchase #5 $51.79   3.620%   $53.6648   $53.66   $53.65   $53.70  
  Purchase #6 $48.37   6.820%   $51.6688   $51.67   $51.65   $51.70  
  Purchase #7 $226.25   4.826%   $237.1688   $237.17   $237.15   $237.20  
  7 purchase totals = $965.22       $1,034.4752   $1,034.48   $1,034.45   $1,034.60