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 $40.84   5.652%   $43.1483   $43.15   $43.15   $43.10  
  Purchase #2 $244.26   5.774%   $258.3636   $258.36   $258.35   $258.40  
  Purchase #3 $101.84   9.303%   $111.3142   $111.31   $111.30   $111.30  
  Purchase #4 $244.25   7.152%   $261.7188   $261.72   $261.70   $261.70  
  Purchase #5 $217.91   8.713%   $236.8965   $236.90   $236.90   $236.90  
  Purchase #6 $11.40   10.588%   $12.607   $12.61   $12.60   $12.60  
  Purchase #7 $43.65   7.245%   $46.8124   $46.81   $46.80   $46.80  
  7 purchase totals = $904.15       $970.8608   $970.86   $970.80   $970.80