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 $45.37   9.452%   $49.6584   $49.66   $49.65   $49.70  
  Purchase #2 $242.81   8.345%   $263.0725   $263.07   $263.05   $263.10  
  Purchase #3 $234.51   8.105%   $253.517   $253.52   $253.50   $253.50  
  Purchase #4 $139.60   10.112%   $153.7164   $153.72   $153.70   $153.70  
  Purchase #5 $226.37   6.458%   $240.989   $240.99   $241.00   $241.00  
  Purchase #6 $163.51   5.492%   $172.49   $172.49   $172.50   $172.50  
  Purchase #7 $67.82   8.422%   $73.5318   $73.53   $73.55   $73.50  
  7 purchase totals = $1,119.99       $1,206.9751   $1,206.98   $1,206.95   $1,207.00