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 $106.99   6.830%   $114.2974   $114.30   $114.30   $114.30  
  Purchase #2 $56.87   8.168%   $61.5151   $61.52   $61.50   $61.50  
  Purchase #3 $44.98   5.201%   $47.3194   $47.32   $47.30   $47.30  
  Purchase #4 $224.46   4.820%   $235.279   $235.28   $235.30   $235.30  
  Purchase #5 $164.46   6.577%   $175.2765   $175.28   $175.30   $175.30  
  Purchase #6 $144.93   5.108%   $152.333   $152.33   $152.35   $152.30  
  Purchase #7 $70.59   5.764%   $74.6588   $74.66   $74.65   $74.70  
  7 purchase totals = $813.28       $860.6792   $860.69   $860.70   $860.70