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 $104.91   11.242%   $116.704   $116.70   $116.70   $116.70  
  Purchase #2 $200.85   3.664%   $208.2091   $208.21   $208.20   $208.20  
  Purchase #3 $151.94   10.173%   $167.3969   $167.40   $167.40   $167.40  
  Purchase #4 $160.63   13.822%   $182.8323   $182.83   $182.85   $182.80  
  Purchase #5 $119.99   4.171%   $124.9948   $124.99   $125.00   $125.00  
  Purchase #6 $230.70   12.515%   $259.5721   $259.57   $259.55   $259.60  
  Purchase #7 $112.44   8.614%   $122.1256   $122.13   $122.15   $122.10  
  7 purchase totals = $1,081.46       $1,181.8348   $1,181.83   $1,181.85   $1,181.80