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 $39.77   8.867%   $43.2964   $43.30   $43.30   $43.30  
  Purchase #2 $175.64   6.116%   $186.3821   $186.38   $186.40   $186.40  
  Purchase #3 $148.29   9.361%   $162.1714   $162.17   $162.15   $162.20  
  Purchase #4 $16.49   9.272%   $18.019   $18.02   $18.00   $18.00  
  Purchase #5 $243.31   5.815%   $257.4585   $257.46   $257.45   $257.50  
  Purchase #6 $227.36   6.597%   $242.3589   $242.36   $242.35   $242.40  
  Purchase #7 $15.26   8.688%   $16.5858   $16.59   $16.60   $16.60  
  7 purchase totals = $866.12       $926.2721   $926.28   $926.25   $926.40