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 $58.58   5.428%   $61.7597   $61.76   $61.75   $61.80  
  Purchase #2 $142.78   11.532%   $159.2454   $159.25   $159.25   $159.20  
  Purchase #3 $105.80   7.523%   $113.7593   $113.76   $113.75   $113.80  
  Purchase #4 $87.52   6.329%   $93.0591   $93.06   $93.05   $93.10  
  Purchase #5 $101.32   11.437%   $112.908   $112.91   $112.90   $112.90  
  Purchase #6 $163.73   11.299%   $182.2299   $182.23   $182.25   $182.20  
  Purchase #7 $124.85   9.318%   $136.4835   $136.48   $136.50   $136.50  
  7 purchase totals = $784.58       $859.4449   $859.45   $859.45   $859.50