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 $53.64   11.806%   $59.9727   $59.97   $59.95   $60.00  
  Purchase #2 $105.57   4.461%   $110.2795   $110.28   $110.30   $110.30  
  Purchase #3 $203.74   4.403%   $212.7107   $212.71   $212.70   $212.70  
  Purchase #4 $248.75   5.682%   $262.884   $262.88   $262.90   $262.90  
  Purchase #5 $126.75   8.696%   $137.7722   $137.77   $137.75   $137.80  
  Purchase #6 $111.38   3.379%   $115.1435   $115.14   $115.15   $115.10  
  Purchase #7 $86.73   10.214%   $95.5886   $95.59   $95.60   $95.60  
  7 purchase totals = $936.56       $994.3512   $994.34   $994.35   $994.40