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 $29.69   10.106%   $32.6905   $32.69   $32.70   $32.70  
  Purchase #2 $68.26   7.322%   $73.258   $73.26   $73.25   $73.30  
  Purchase #3 $61.59   9.560%   $67.478   $67.48   $67.50   $67.50  
  Purchase #4 $239.45   12.448%   $269.2567   $269.26   $269.25   $269.30  
  Purchase #5 $236.68   11.523%   $263.9526   $263.95   $263.95   $264.00  
  Purchase #6 $16.74   6.206%   $17.7789   $17.78   $17.80   $17.80  
  Purchase #7 $49.56   8.176%   $53.612   $53.61   $53.60   $53.60  
  7 purchase totals = $701.97       $778.0267   $778.03   $778.05   $778.20