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 $61.36   7.662%   $66.0614   $66.06   $66.05   $66.10  
  Purchase #2 $178.67   6.860%   $190.9268   $190.93   $190.95   $190.90  
  Purchase #3 $137.90   10.609%   $152.5298   $152.53   $152.55   $152.50  
  Purchase #4 $105.40   7.737%   $113.5548   $113.55   $113.55   $113.60  
  Purchase #5 $244.42   3.285%   $252.4492   $252.45   $252.45   $252.40  
  Purchase #6 $183.84   8.442%   $199.3598   $199.36   $199.35   $199.40  
  Purchase #7 $219.51   13.481%   $249.1021   $249.10   $249.10   $249.10  
  7 purchase totals = $1,131.10       $1,223.9839   $1,223.98   $1,224.00   $1,224.00