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 $58.55   12.768%   $66.0257   $66.03   $66.05   $66.00  
  Purchase #2 $248.55   10.212%   $273.9319   $273.93   $273.95   $273.90  
  Purchase #3 $47.55   6.155%   $50.4767   $50.48   $50.50   $50.50  
  Purchase #4 $35.93   5.164%   $37.7854   $37.79   $37.80   $37.80  
  Purchase #5 $196.46   4.463%   $205.228   $205.23   $205.25   $205.20  
  Purchase #6 $59.94   3.729%   $62.1752   $62.18   $62.20   $62.20  
  Purchase #7 $213.81   12.114%   $239.7109   $239.71   $239.70   $239.70  
  7 purchase totals = $860.79       $935.3338   $935.35   $935.45   $935.30