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 $57.72   8.234%   $62.4727   $62.47   $62.45   $62.50  
  Purchase #2 $174.54   3.791%   $181.1568   $181.16   $181.15   $181.20  
  Purchase #3 $64.68   8.212%   $69.9915   $69.99   $70.00   $70.00  
  Purchase #4 $87.65   6.411%   $93.2692   $93.27   $93.25   $93.30  
  Purchase #5 $164.66   13.691%   $187.2036   $187.20   $187.20   $187.20  
  Purchase #6 $68.46   13.467%   $77.6795   $77.68   $77.70   $77.70  
  Purchase #7 $9.25   4.723%   $9.6869   $9.69   $9.70   $9.70  
  7 purchase totals = $626.96       $681.4602   $681.46   $681.45   $681.60