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 $172.86   11.609%   $192.9273   $192.93   $192.95   $192.90  
  Purchase #2 $238.57   11.348%   $265.6429   $265.64   $265.65   $265.60  
  Purchase #3 $172.62   11.673%   $192.7699   $192.77   $192.75   $192.80  
  Purchase #4 $165.87   12.469%   $186.5523   $186.55   $186.55   $186.60  
  Purchase #5 $195.83   5.732%   $207.055   $207.06   $207.05   $207.10  
  Purchase #6 $69.55   6.692%   $74.2043   $74.20   $74.20   $74.20  
  Purchase #7 $35.73   5.242%   $37.603   $37.60   $37.60   $37.60  
  7 purchase totals = $1,051.03       $1,156.7547   $1,156.75   $1,156.75   $1,156.80