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 $192.48   12.370%   $216.2898   $216.29   $216.30   $216.30  
  Purchase #2 $94.46   13.748%   $107.4464   $107.45   $107.45   $107.40  
  Purchase #3 $185.43   12.484%   $208.5791   $208.58   $208.60   $208.60  
  Purchase #4 $49.49   6.494%   $52.7039   $52.70   $52.70   $52.70  
  Purchase #5 $208.68   3.744%   $216.493   $216.49   $216.50   $216.50  
  Purchase #6 $231.79   6.170%   $246.0914   $246.09   $246.10   $246.10  
  Purchase #7 $13.63   5.824%   $14.4238   $14.42   $14.40   $14.40  
  7 purchase totals = $975.96       $1,062.0274   $1,062.02   $1,062.05   $1,062.00