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 $208.74   10.692%   $231.0585   $231.06   $231.05   $231.10  
  Purchase #2 $192.67   8.110%   $208.2955   $208.30   $208.30   $208.30  
  Purchase #3 $52.99   8.618%   $57.5567   $57.56   $57.55   $57.60  
  Purchase #4 $222.91   7.462%   $239.5435   $239.54   $239.55   $239.50  
  Purchase #5 $46.80   11.124%   $52.006   $52.01   $52.00   $52.00  
  Purchase #6 $22.65   12.446%   $25.469   $25.47   $25.45   $25.50  
  Purchase #7 $59.55   11.131%   $66.1785   $66.18   $66.20   $66.20  
  7 purchase totals = $806.31       $880.1077   $880.12   $880.10   $880.20