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 $145.88   12.429%   $164.0114   $164.01   $164.00   $164.00  
  Purchase #2 $212.60   7.260%   $228.0348   $228.03   $228.05   $228.00  
  Purchase #3 $53.44   10.228%   $58.9058   $58.91   $58.90   $58.90  
  Purchase #4 $52.35   12.619%   $58.956   $58.96   $58.95   $59.00  
  Purchase #5 $133.68   4.342%   $139.4844   $139.48   $139.50   $139.50  
  Purchase #6 $180.34   8.271%   $195.2559   $195.26   $195.25   $195.30  
  Purchase #7 $207.92   9.132%   $226.9073   $226.91   $226.90   $226.90  
  7 purchase totals = $986.21       $1,071.5556   $1,071.56   $1,071.55   $1,071.60