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 $84.96   11.679%   $94.8825   $94.88   $94.90   $94.90  
  Purchase #2 $127.64   6.729%   $136.2289   $136.23   $136.25   $136.20  
  Purchase #3 $61.96   12.341%   $69.6065   $69.61   $69.60   $69.60  
  Purchase #4 $22.51   5.719%   $23.7973   $23.80   $23.80   $23.80  
  Purchase #5 $117.86   9.112%   $128.5994   $128.60   $128.60   $128.60  
  Purchase #6 $104.62   12.817%   $118.0291   $118.03   $118.05   $118.00  
  Purchase #7 $185.34   3.439%   $191.7138   $191.71   $191.70   $191.70  
  7 purchase totals = $704.89       $762.8575   $762.86   $762.90   $762.80