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 $21.92   13.451%   $24.8685   $24.87   $24.85   $24.90  
  Purchase #2 $175.51   3.261%   $181.2334   $181.23   $181.25   $181.20  
  Purchase #3 $46.77   13.245%   $52.9647   $52.96   $52.95   $53.00  
  Purchase #4 $88.39   3.522%   $91.5031   $91.50   $91.50   $91.50  
  Purchase #5 $196.57   12.245%   $220.64   $220.64   $220.65   $220.60  
  Purchase #6 $164.56   13.632%   $186.9928   $186.99   $187.00   $187.00  
  Purchase #7 $203.70   3.833%   $211.5078   $211.51   $211.50   $211.50  
  7 purchase totals = $897.42       $969.7103   $969.70   $969.70   $969.70