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 $33.35   7.596%   $35.8833   $35.88   $35.90   $35.90  
  Purchase #2 $113.66   11.160%   $126.3445   $126.34   $126.35   $126.30  
  Purchase #3 $95.91   12.544%   $107.941   $107.94   $107.95   $107.90  
  Purchase #4 $69.42   10.716%   $76.859   $76.86   $76.85   $76.90  
  Purchase #5 $122.60   5.699%   $129.587   $129.59   $129.60   $129.60  
  Purchase #6 $30.40   12.141%   $34.0909   $34.09   $34.10   $34.10  
  Purchase #7 $50.91   12.634%   $57.342   $57.34   $57.35   $57.30  
  7 purchase totals = $516.25       $568.0477   $568.04   $568.10   $568.00