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 $166.86   10.561%   $184.4821   $184.48   $184.50   $184.50  
  Purchase #2 $67.59   3.529%   $69.9753   $69.98   $70.00   $70.00  
  Purchase #3 $241.82   11.531%   $269.7043   $269.70   $269.70   $269.70  
  Purchase #4 $56.87   11.593%   $63.4629   $63.46   $63.45   $63.50  
  Purchase #5 $17.26   10.247%   $19.0286   $19.03   $19.05   $19.00  
  Purchase #6 $24.73   8.409%   $26.8095   $26.81   $26.80   $26.80  
  Purchase #7 $185.81   4.178%   $193.5731   $193.57   $193.55   $193.60  
  7 purchase totals = $760.94       $827.0358   $827.03   $827.05   $827.10