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 $217.70   11.213%   $242.1107   $242.11   $242.10   $242.10  
  Purchase #2 $55.54   9.401%   $60.7613   $60.76   $60.75   $60.80  
  Purchase #3 $222.49   3.690%   $230.6999   $230.70   $230.70   $230.70  
  Purchase #4 $167.77   11.334%   $186.7851   $186.79   $186.80   $186.80  
  Purchase #5 $154.37   3.332%   $159.5136   $159.51   $159.50   $159.50  
  Purchase #6 $33.89   13.550%   $38.4821   $38.48   $38.50   $38.50  
  Purchase #7 $129.95   4.380%   $135.6418   $135.64   $135.65   $135.60  
  7 purchase totals = $981.71       $1,053.9945   $1,053.99   $1,054.00   $1,054.00