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 $203.28   6.570%   $216.6355   $216.64   $216.65   $216.60  
  Purchase #2 $249.79   5.525%   $263.5909   $263.59   $263.60   $263.60  
  Purchase #3 $74.69   6.202%   $79.3223   $79.32   $79.30   $79.30  
  Purchase #4 $248.69   9.351%   $271.945   $271.95   $271.95   $271.90  
  Purchase #5 $66.39   10.560%   $73.4008   $73.40   $73.40   $73.40  
  Purchase #6 $170.55   11.769%   $190.622   $190.62   $190.60   $190.60  
  Purchase #7 $60.60   10.493%   $66.9588   $66.96   $66.95   $67.00  
  7 purchase totals = $1,073.99       $1,162.4753   $1,162.48   $1,162.45   $1,162.40