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 $225.27   7.124%   $241.3182   $241.32   $241.30   $241.30  
  Purchase #2 $183.83   9.696%   $201.6542   $201.65   $201.65   $201.70  
  Purchase #3 $15.41   11.795%   $17.2276   $17.23   $17.25   $17.20  
  Purchase #4 $35.73   13.565%   $40.5768   $40.58   $40.60   $40.60  
  Purchase #5 $179.72   3.464%   $185.9455   $185.95   $185.95   $185.90  
  Purchase #6 $162.60   3.115%   $167.665   $167.67   $167.65   $167.70  
  Purchase #7 $87.58   11.619%   $97.7559   $97.76   $97.75   $97.80  
  7 purchase totals = $890.14       $952.1432   $952.16   $952.15   $952.20