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 $56.47   12.423%   $63.4853   $63.49   $63.50   $63.50  
  Purchase #2 $205.47   3.549%   $212.7621   $212.76   $212.75   $212.80  
  Purchase #3 $217.46   4.354%   $226.9282   $226.93   $226.95   $226.90  
  Purchase #4 $6.83   4.333%   $7.1259   $7.13   $7.15   $7.10  
  Purchase #5 $200.44   12.592%   $225.6794   $225.68   $225.70   $225.70  
  Purchase #6 $213.70   12.257%   $239.8932   $239.89   $239.90   $239.90  
  Purchase #7 $160.82   5.215%   $169.2068   $169.21   $169.20   $169.20  
  7 purchase totals = $1,061.19       $1,145.0809   $1,145.09   $1,145.15   $1,145.10