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 $61.61   13.124%   $69.6957   $69.70   $69.70   $69.70  
  Purchase #2 $221.46   9.255%   $241.9561   $241.96   $241.95   $242.00  
  Purchase #3 $21.61   6.608%   $23.038   $23.04   $23.05   $23.00  
  Purchase #4 $190.68   6.245%   $202.588   $202.59   $202.60   $202.60  
  Purchase #5 $44.62   9.536%   $48.875   $48.88   $48.90   $48.90  
  Purchase #6 $168.97   8.704%   $183.6771   $183.68   $183.70   $183.70  
  Purchase #7 $210.64   6.590%   $224.5212   $224.52   $224.50   $224.50  
  7 purchase totals = $919.59       $994.3511   $994.37   $994.40   $994.40