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 $67.52   13.539%   $76.6615   $76.66   $76.65   $76.70  
  Purchase #2 $230.50   7.102%   $246.8701   $246.87   $246.85   $246.90  
  Purchase #3 $70.55   8.473%   $76.5277   $76.53   $76.55   $76.50  
  Purchase #4 $237.94   10.252%   $262.3336   $262.33   $262.35   $262.30  
  Purchase #5 $17.80   3.502%   $18.4234   $18.42   $18.40   $18.40  
  Purchase #6 $158.40   3.632%   $164.1531   $164.15   $164.15   $164.20  
  Purchase #7 $235.64   11.473%   $262.675   $262.68   $262.70   $262.70  
  7 purchase totals = $1,018.35       $1,107.6444   $1,107.64   $1,107.65   $1,107.70