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 $239.36   5.577%   $252.7091   $252.71   $252.70   $252.70  
  Purchase #2 $183.53   12.171%   $205.8674   $205.87   $205.85   $205.90  
  Purchase #3 $157.35   13.361%   $178.3735   $178.37   $178.35   $178.40  
  Purchase #4 $246.82   12.611%   $277.9465   $277.95   $277.95   $277.90  
  Purchase #5 $165.53   3.246%   $170.9031   $170.90   $170.90   $170.90  
  Purchase #6 $52.95   13.429%   $60.0607   $60.06   $60.05   $60.10  
  Purchase #7 $161.68   13.611%   $183.6863   $183.69   $183.70   $183.70  
  7 purchase totals = $1,207.22       $1,329.5466   $1,329.55   $1,329.50   $1,329.60