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 $74.61   8.510%   $80.9593   $80.96   $80.95   $81.00  
  Purchase #2 $223.39   11.217%   $248.4477   $248.45   $248.45   $248.40  
  Purchase #3 $101.71   12.220%   $114.139   $114.14   $114.15   $114.10  
  Purchase #4 $94.47   4.290%   $98.5228   $98.52   $98.50   $98.50  
  Purchase #5 $224.44   12.128%   $251.6601   $251.66   $251.65   $251.70  
  Purchase #6 $120.44   7.837%   $129.8789   $129.88   $129.90   $129.90  
  Purchase #7 $22.57   4.773%   $23.6473   $23.65   $23.65   $23.60  
  7 purchase totals = $861.63       $947.2551   $947.26   $947.25   $947.20