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 $46.41   13.387%   $52.6229   $52.62   $52.60   $52.60  
  Purchase #2 $143.76   7.150%   $154.0388   $154.04   $154.05   $154.00  
  Purchase #3 $85.66   3.195%   $88.3968   $88.40   $88.40   $88.40  
  Purchase #4 $248.65   8.182%   $268.9945   $268.99   $269.00   $269.00  
  Purchase #5 $24.80   3.308%   $25.6204   $25.62   $25.60   $25.60  
  Purchase #6 $82.65   8.559%   $89.724   $89.72   $89.70   $89.70  
  Purchase #7 $126.30   7.119%   $135.2913   $135.29   $135.30   $135.30  
  7 purchase totals = $758.23       $814.6887   $814.68   $814.65   $814.60