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 $62.54   9.806%   $68.6727   $68.67   $68.65   $68.70  
  Purchase #2 $141.87   6.766%   $151.4689   $151.47   $151.45   $151.50  
  Purchase #3 $183.66   8.118%   $198.5695   $198.57   $198.55   $198.60  
  Purchase #4 $173.49   10.603%   $191.8851   $191.89   $191.90   $191.90  
  Purchase #5 $119.40   8.380%   $129.4057   $129.41   $129.40   $129.40  
  Purchase #6 $83.73   11.767%   $93.5825   $93.58   $93.60   $93.60  
  Purchase #7 $154.61   6.615%   $164.8375   $164.84   $164.85   $164.80  
  7 purchase totals = $919.30       $998.4219   $998.43   $998.40   $998.50