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 $246.91   5.200%   $259.7493   $259.75   $259.75   $259.70  
  Purchase #2 $144.91   6.104%   $153.7553   $153.76   $153.75   $153.80  
  Purchase #3 $218.63   9.154%   $238.6434   $238.64   $238.65   $238.60  
  Purchase #4 $204.85   8.744%   $222.7621   $222.76   $222.75   $222.80  
  Purchase #5 $61.59   3.347%   $63.6514   $63.65   $63.65   $63.70  
  Purchase #6 $56.41   8.366%   $61.1293   $61.13   $61.15   $61.10  
  Purchase #7 $129.80   5.509%   $136.9507   $136.95   $136.95   $137.00  
  7 purchase totals = $1,063.10       $1,136.6415   $1,136.64   $1,136.65   $1,136.70