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 $70.65   8.404%   $76.5874   $76.59   $76.60   $76.60  
  Purchase #2 $249.51   6.335%   $265.3165   $265.32   $265.30   $265.30  
  Purchase #3 $5.94   4.593%   $6.2128   $6.21   $6.20   $6.20  
  Purchase #4 $211.58   3.619%   $219.2371   $219.24   $219.25   $219.20  
  Purchase #5 $34.91   11.136%   $38.7976   $38.80   $38.80   $38.80  
  Purchase #6 $234.45   12.802%   $264.4643   $264.46   $264.45   $264.50  
  Purchase #7 $140.38   13.325%   $159.0856   $159.09   $159.10   $159.10  
  7 purchase totals = $947.42       $1,029.7013   $1,029.71   $1,029.70   $1,029.70