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 $216.27   5.739%   $228.6817   $228.68   $228.70   $228.70  
  Purchase #2 $92.79   3.609%   $96.1388   $96.14   $96.15   $96.10  
  Purchase #3 $53.29   10.488%   $58.8791   $58.88   $58.90   $58.90  
  Purchase #4 $76.30   7.220%   $81.8089   $81.81   $81.80   $81.80  
  Purchase #5 $51.76   5.528%   $54.6213   $54.62   $54.60   $54.60  
  Purchase #6 $100.88   5.796%   $106.727   $106.73   $106.75   $106.70  
  Purchase #7 $43.94   11.615%   $49.0436   $49.04   $49.05   $49.00  
  7 purchase totals = $635.23       $675.9004   $675.90   $675.95   $675.80