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 $244.76   3.566%   $253.4881   $253.49   $253.50   $253.50  
  Purchase #2 $110.99   5.107%   $116.6583   $116.66   $116.65   $116.70  
  Purchase #3 $24.43   10.195%   $26.9206   $26.92   $26.90   $26.90  
  Purchase #4 $171.96   6.506%   $183.1477   $183.15   $183.15   $183.10  
  Purchase #5 $109.75   3.612%   $113.7142   $113.71   $113.70   $113.70  
  Purchase #6 $134.38   9.239%   $146.7954   $146.80   $146.80   $146.80  
  Purchase #7 $127.97   5.616%   $135.1568   $135.16   $135.15   $135.20  
  7 purchase totals = $924.24       $975.8811   $975.89   $975.85   $975.90