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 $59.87   13.522%   $67.9656   $67.97   $67.95   $68.00  
  Purchase #2 $215.58   11.557%   $240.4946   $240.49   $240.50   $240.50  
  Purchase #3 $96.50   9.828%   $105.984   $105.98   $106.00   $106.00  
  Purchase #4 $250.36   9.470%   $274.0691   $274.07   $274.05   $274.10  
  Purchase #5 $72.81   11.623%   $81.2727   $81.27   $81.25   $81.30  
  Purchase #6 $151.41   7.265%   $162.4099   $162.41   $162.40   $162.40  
  Purchase #7 $6.28   7.305%   $6.7388   $6.74   $6.75   $6.70  
  7 purchase totals = $852.81       $938.9347   $938.93   $938.90   $939.00