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 $141.26   7.730%   $152.1794   $152.18   $152.20   $152.20  
  Purchase #2 $231.91   11.227%   $257.9465   $257.95   $257.95   $257.90  
  Purchase #3 $143.99   10.227%   $158.7159   $158.72   $158.70   $158.70  
  Purchase #4 $64.92   7.331%   $69.6793   $69.68   $69.70   $69.70  
  Purchase #5 $35.70   3.826%   $37.0659   $37.07   $37.05   $37.10  
  Purchase #6 $221.93   3.291%   $229.2337   $229.23   $229.25   $229.20  
  Purchase #7 $107.49   13.137%   $121.611   $121.61   $121.60   $121.60  
  7 purchase totals = $947.20       $1,026.4317   $1,026.44   $1,026.45   $1,026.40