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 $67.70   8.699%   $73.5892   $73.59   $73.60   $73.60  
  Purchase #2 $46.68   5.716%   $49.3482   $49.35   $49.35   $49.30  
  Purchase #3 $25.90   4.716%   $27.1214   $27.12   $27.10   $27.10  
  Purchase #4 $18.59   7.589%   $20.0008   $20.00   $20.00   $20.00  
  Purchase #5 $38.82   3.302%   $40.1018   $40.10   $40.10   $40.10  
  Purchase #6 $147.60   6.392%   $157.0346   $157.03   $157.05   $157.00  
  Purchase #7 $73.28   4.688%   $76.7154   $76.72   $76.70   $76.70  
  7 purchase totals = $418.57       $443.9114   $443.91   $443.90   $443.80