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 $96.65   5.282%   $101.7551   $101.76   $101.75   $101.80  
  Purchase #2 $23.63   7.376%   $25.3729   $25.37   $25.35   $25.40  
  Purchase #3 $184.74   12.623%   $208.0597   $208.06   $208.05   $208.10  
  Purchase #4 $212.79   8.514%   $230.9069   $230.91   $230.90   $230.90  
  Purchase #5 $99.83   3.341%   $103.1653   $103.17   $103.15   $103.20  
  Purchase #6 $77.25   9.358%   $84.4791   $84.48   $84.50   $84.50  
  Purchase #7 $171.87   12.667%   $193.6408   $193.64   $193.65   $193.60  
  7 purchase totals = $866.76       $947.3798   $947.39   $947.35   $947.50