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 $162.89   13.695%   $185.1978   $185.20   $185.20   $185.20  
  Purchase #2 $111.60   7.614%   $120.0972   $120.10   $120.10   $120.10  
  Purchase #3 $60.85   10.102%   $66.9971   $67.00   $67.00   $67.00  
  Purchase #4 $191.88   8.749%   $208.6676   $208.67   $208.65   $208.70  
  Purchase #5 $49.57   11.467%   $55.2542   $55.25   $55.25   $55.30  
  Purchase #6 $113.76   12.194%   $127.6319   $127.63   $127.65   $127.60  
  Purchase #7 $233.53   11.436%   $260.2365   $260.24   $260.25   $260.20  
  7 purchase totals = $924.08       $1,024.0823   $1,024.09   $1,024.10   $1,024.10