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 $53.86   8.138%   $58.2431   $58.24   $58.25   $58.20  
  Purchase #2 $195.88   9.520%   $214.5278   $214.53   $214.55   $214.50  
  Purchase #3 $125.77   8.491%   $136.4491   $136.45   $136.45   $136.40  
  Purchase #4 $115.91   9.416%   $126.8241   $126.82   $126.80   $126.80  
  Purchase #5 $192.99   8.577%   $209.5428   $209.54   $209.55   $209.50  
  Purchase #6 $201.54   10.802%   $223.3104   $223.31   $223.30   $223.30  
  Purchase #7 $236.85   11.331%   $263.6875   $263.69   $263.70   $263.70  
  7 purchase totals = $1,122.80       $1,232.5848   $1,232.58   $1,232.60   $1,232.40