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 $235.50   10.683%   $260.6585   $260.66   $260.65   $260.70  
  Purchase #2 $208.70   12.572%   $234.9378   $234.94   $234.95   $234.90  
  Purchase #3 $159.51   13.325%   $180.7647   $180.76   $180.75   $180.80  
  Purchase #4 $38.93   7.796%   $41.965   $41.97   $41.95   $42.00  
  Purchase #5 $235.80   5.414%   $248.5662   $248.57   $248.55   $248.60  
  Purchase #6 $240.99   7.843%   $259.8908   $259.89   $259.90   $259.90  
  Purchase #7 $32.87   5.769%   $34.7663   $34.77   $34.75   $34.80  
  7 purchase totals = $1,152.30       $1,261.5493   $1,261.56   $1,261.50   $1,261.70