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 $89.67   3.593%   $92.8918   $92.89   $92.90   $92.90  
  Purchase #2 $147.84   9.513%   $161.904   $161.90   $161.90   $161.90  
  Purchase #3 $67.89   3.157%   $70.0333   $70.03   $70.05   $70.00  
  Purchase #4 $54.29   12.679%   $61.1734   $61.17   $61.15   $61.20  
  Purchase #5 $98.28   3.149%   $101.3748   $101.37   $101.35   $101.40  
  Purchase #6 $211.36   9.403%   $231.2342   $231.23   $231.25   $231.20  
  Purchase #7 $214.96   8.602%   $233.4509   $233.45   $233.45   $233.50  
  7 purchase totals = $884.29       $952.0624   $952.04   $952.05   $952.10