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 $64.65   10.318%   $71.3206   $71.32   $71.30   $71.30  
  Purchase #2 $239.49   11.324%   $266.6098   $266.61   $266.60   $266.60  
  Purchase #3 $10.35   11.714%   $11.5624   $11.56   $11.55   $11.60  
  Purchase #4 $154.80   12.701%   $174.4611   $174.46   $174.45   $174.50  
  Purchase #5 $59.68   5.783%   $63.1313   $63.13   $63.15   $63.10  
  Purchase #6 $190.35   5.104%   $200.0655   $200.07   $200.05   $200.10  
  Purchase #7 $105.26   11.381%   $117.2396   $117.24   $117.25   $117.20  
  7 purchase totals = $824.58       $904.3903   $904.39   $904.35   $904.40