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 $144.28   11.712%   $161.1781   $161.18   $161.20   $161.20  
  Purchase #2 $195.51   7.174%   $209.5359   $209.54   $209.55   $209.50  
  Purchase #3 $35.48   8.216%   $38.395   $38.40   $38.40   $38.40  
  Purchase #4 $24.62   11.182%   $27.373   $27.37   $27.35   $27.40  
  Purchase #5 $195.32   13.502%   $221.6921   $221.69   $221.70   $221.70  
  Purchase #6 $182.37   11.552%   $203.4374   $203.44   $203.45   $203.40  
  Purchase #7 $105.29   11.507%   $117.4057   $117.41   $117.40   $117.40  
  7 purchase totals = $882.87       $979.0172   $979.03   $979.05   $979.00