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 $192.59   7.256%   $206.5643   $206.56   $206.55   $206.60  
  Purchase #2 $94.93   4.339%   $99.049   $99.05   $99.05   $99.00  
  Purchase #3 $185.66   13.335%   $210.4178   $210.42   $210.40   $210.40  
  Purchase #4 $15.32   4.120%   $15.9512   $15.95   $15.95   $16.00  
  Purchase #5 $58.46   7.164%   $62.6481   $62.65   $62.65   $62.60  
  Purchase #6 $71.46   11.163%   $79.4371   $79.44   $79.45   $79.40  
  Purchase #7 $171.79   8.543%   $186.466   $186.47   $186.45   $186.50  
  7 purchase totals = $790.21       $860.5335   $860.54   $860.50   $860.50