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 $93.52   3.684%   $96.9653   $96.97   $96.95   $97.00  
  Purchase #2 $73.90   10.459%   $81.6292   $81.63   $81.65   $81.60  
  Purchase #3 $201.67   3.552%   $208.8333   $208.83   $208.85   $208.80  
  Purchase #4 $36.36   3.396%   $37.5948   $37.59   $37.60   $37.60  
  Purchase #5 $23.75   9.247%   $25.9462   $25.95   $25.95   $25.90  
  Purchase #6 $232.74   4.386%   $242.948   $242.95   $242.95   $242.90  
  Purchase #7 $140.66   10.247%   $155.0734   $155.07   $155.05   $155.10  
  7 purchase totals = $802.60       $848.9902   $848.99   $849.00   $848.90