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 $58.45   12.369%   $65.6797   $65.68   $65.70   $65.70  
  Purchase #2 $228.37   13.719%   $259.7001   $259.70   $259.70   $259.70  
  Purchase #3 $195.49   11.487%   $217.9459   $217.95   $217.95   $217.90  
  Purchase #4 $84.40   5.291%   $88.8656   $88.87   $88.85   $88.90  
  Purchase #5 $195.47   5.642%   $206.4984   $206.50   $206.50   $206.50  
  Purchase #6 $47.83   9.646%   $52.4437   $52.44   $52.45   $52.40  
  Purchase #7 $219.67   8.297%   $237.896   $237.90   $237.90   $237.90  
  7 purchase totals = $1,029.68       $1,129.0294   $1,129.04   $1,129.05   $1,129.00