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 $43.77   7.329%   $46.9779   $46.98   $47.00   $47.00  
  Purchase #2 $226.54   13.285%   $256.6358   $256.64   $256.65   $256.60  
  Purchase #3 $85.96   11.118%   $95.517   $95.52   $95.50   $95.50  
  Purchase #4 $81.47   3.176%   $84.0575   $84.06   $84.05   $84.10  
  Purchase #5 $119.61   4.462%   $124.947   $124.95   $124.95   $124.90  
  Purchase #6 $207.88   11.794%   $232.3974   $232.40   $232.40   $232.40  
  Purchase #7 $11.99   6.409%   $12.7584   $12.76   $12.75   $12.80  
  7 purchase totals = $777.22       $853.2910   $853.31   $853.30   $853.30