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 $160.53   10.522%   $177.421   $177.42   $177.40   $177.40  
  Purchase #2 $7.31   4.655%   $7.6503   $7.65   $7.65   $7.70  
  Purchase #3 $89.92   3.772%   $93.3118   $93.31   $93.30   $93.30  
  Purchase #4 $26.72   12.367%   $30.0245   $30.02   $30.00   $30.00  
  Purchase #5 $26.50   11.333%   $29.5032   $29.50   $29.50   $29.50  
  Purchase #6 $30.77   12.372%   $34.5769   $34.58   $34.60   $34.60  
  Purchase #7 $186.60   13.225%   $211.2779   $211.28   $211.30   $211.30  
  7 purchase totals = $528.35       $583.7656   $583.76   $583.75   $583.80