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 $248.28   8.496%   $269.3739   $269.37   $269.35   $269.40  
  Purchase #2 $41.87   9.757%   $45.9553   $45.96   $45.95   $46.00  
  Purchase #3 $159.81   3.278%   $165.0486   $165.05   $165.05   $165.00  
  Purchase #4 $229.41   5.406%   $241.8119   $241.81   $241.80   $241.80  
  Purchase #5 $31.66   7.873%   $34.1526   $34.15   $34.15   $34.20  
  Purchase #6 $37.86   11.685%   $42.2839   $42.28   $42.30   $42.30  
  Purchase #7 $62.65   6.838%   $66.934   $66.93   $66.95   $66.90  
  7 purchase totals = $811.54       $865.5602   $865.55   $865.55   $865.60