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 $186.56   13.786%   $212.2792   $212.28   $212.30   $212.30  
  Purchase #2 $137.43   13.182%   $155.546   $155.55   $155.55   $155.50  
  Purchase #3 $227.99   6.255%   $242.2508   $242.25   $242.25   $242.30  
  Purchase #4 $190.76   5.346%   $200.958   $200.96   $200.95   $201.00  
  Purchase #5 $139.38   5.536%   $147.0961   $147.10   $147.10   $147.10  
  Purchase #6 $48.42   13.800%   $55.102   $55.10   $55.10   $55.10  
  Purchase #7 $171.41   12.385%   $192.6391   $192.64   $192.65   $192.60  
  7 purchase totals = $1,101.95       $1,205.8712   $1,205.88   $1,205.90   $1,205.90