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 $64.30   6.653%   $68.5779   $68.58   $68.60   $68.60  
  Purchase #2 $93.93   12.176%   $105.3669   $105.37   $105.35   $105.40  
  Purchase #3 $51.62   13.550%   $58.6145   $58.61   $58.60   $58.60  
  Purchase #4 $223.93   11.107%   $248.8019   $248.80   $248.80   $248.80  
  Purchase #5 $200.61   3.339%   $207.3084   $207.31   $207.30   $207.30  
  Purchase #6 $111.32   11.853%   $124.5148   $124.51   $124.50   $124.50  
  Purchase #7 $144.40   5.756%   $152.7117   $152.71   $152.70   $152.70  
  7 purchase totals = $890.11       $965.8961   $965.89   $965.85   $965.90