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 $61.68   11.331%   $68.669   $68.67   $68.65   $68.70  
  Purchase #2 $119.26   4.304%   $124.393   $124.39   $124.40   $124.40  
  Purchase #3 $146.76   3.602%   $152.0463   $152.05   $152.05   $152.00  
  Purchase #4 $35.62   6.131%   $37.8039   $37.80   $37.80   $37.80  
  Purchase #5 $118.73   7.340%   $127.4448   $127.44   $127.45   $127.40  
  Purchase #6 $24.94   7.407%   $26.7873   $26.79   $26.80   $26.80  
  Purchase #7 $8.90   11.762%   $9.9468   $9.95   $9.95   $9.90  
  7 purchase totals = $515.89       $547.0911   $547.09   $547.10   $547.00