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 $84.53   4.793%   $88.5815   $88.58   $88.60   $88.60  
  Purchase #2 $157.31   9.190%   $171.7668   $171.77   $171.75   $171.80  
  Purchase #3 $71.45   7.243%   $76.6251   $76.63   $76.65   $76.60  
  Purchase #4 $221.77   4.566%   $231.896   $231.90   $231.90   $231.90  
  Purchase #5 $154.70   12.188%   $173.5548   $173.55   $173.55   $173.60  
  Purchase #6 $232.76   13.105%   $263.2632   $263.26   $263.25   $263.30  
  Purchase #7 $129.25   13.488%   $146.6832   $146.68   $146.70   $146.70  
  7 purchase totals = $1,051.77       $1,152.3706   $1,152.37   $1,152.40   $1,152.50