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 $71.37   8.233%   $77.2459   $77.25   $77.25   $77.20  
  Purchase #2 $239.42   11.192%   $266.2159   $266.22   $266.20   $266.20  
  Purchase #3 $177.53   10.398%   $195.9896   $195.99   $196.00   $196.00  
  Purchase #4 $121.95   11.506%   $135.9816   $135.98   $136.00   $136.00  
  Purchase #5 $48.65   11.730%   $54.3566   $54.36   $54.35   $54.40  
  Purchase #6 $95.89   8.141%   $103.6964   $103.70   $103.70   $103.70  
  Purchase #7 $25.86   8.570%   $28.0762   $28.08   $28.10   $28.10  
  7 purchase totals = $780.67       $861.5622   $861.58   $861.60   $861.60