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 $65.54   4.687%   $68.6119   $68.61   $68.60   $68.60  
  Purchase #2 $68.91   12.336%   $77.4107   $77.41   $77.40   $77.40  
  Purchase #3 $108.25   10.588%   $119.7115   $119.71   $119.70   $119.70  
  Purchase #4 $153.36   4.148%   $159.7214   $159.72   $159.70   $159.70  
  Purchase #5 $36.85   5.452%   $38.8591   $38.86   $38.85   $38.90  
  Purchase #6 $185.97   10.600%   $205.6828   $205.68   $205.70   $205.70  
  Purchase #7 $114.75   10.499%   $126.7976   $126.80   $126.80   $126.80  
  7 purchase totals = $733.63       $796.7950   $796.79   $796.75   $796.80