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 $62.49   9.171%   $68.221   $68.22   $68.20   $68.20  
  Purchase #2 $35.44   4.480%   $37.0277   $37.03   $37.05   $37.00  
  Purchase #3 $214.85   6.151%   $228.0654   $228.07   $228.05   $228.10  
  Purchase #4 $64.86   11.646%   $72.4136   $72.41   $72.40   $72.40  
  Purchase #5 $49.39   13.695%   $56.154   $56.15   $56.15   $56.20  
  Purchase #6 $244.70   5.671%   $258.5769   $258.58   $258.60   $258.60  
  Purchase #7 $139.60   5.870%   $147.7945   $147.79   $147.80   $147.80  
  7 purchase totals = $811.33       $868.2531   $868.25   $868.25   $868.30