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 $55.69   8.541%   $60.4465   $60.45   $60.45   $60.40  
  Purchase #2 $168.84   3.151%   $174.1601   $174.16   $174.15   $174.20  
  Purchase #3 $183.85   8.180%   $198.8889   $198.89   $198.90   $198.90  
  Purchase #4 $68.41   6.794%   $73.0578   $73.06   $73.05   $73.10  
  Purchase #5 $106.43   10.154%   $117.2369   $117.24   $117.25   $117.20  
  Purchase #6 $9.80   8.671%   $10.6498   $10.65   $10.65   $10.60  
  Purchase #7 $65.83   7.828%   $70.9832   $70.98   $71.00   $71.00  
  7 purchase totals = $658.85       $705.4232   $705.43   $705.45   $705.40