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 $142.62   12.590%   $160.5759   $160.58   $160.60   $160.60  
  Purchase #2 $237.69   12.713%   $267.9075   $267.91   $267.90   $267.90  
  Purchase #3 $129.67   13.158%   $146.732   $146.73   $146.75   $146.70  
  Purchase #4 $81.56   5.787%   $86.2799   $86.28   $86.30   $86.30  
  Purchase #5 $85.83   12.464%   $96.5279   $96.53   $96.55   $96.50  
  Purchase #6 $243.25   7.465%   $261.4086   $261.41   $261.40   $261.40  
  Purchase #7 $49.52   12.386%   $55.6535   $55.65   $55.65   $55.70  
  7 purchase totals = $970.14       $1,075.0853   $1,075.09   $1,075.15   $1,075.10