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 $24.90   5.734%   $26.3278   $26.33   $26.35   $26.30  
  Purchase #2 $221.58   7.206%   $237.5471   $237.55   $237.55   $237.50  
  Purchase #3 $19.48   8.153%   $21.0682   $21.07   $21.05   $21.10  
  Purchase #4 $126.78   6.368%   $134.8534   $134.85   $134.85   $134.90  
  Purchase #5 $193.76   8.268%   $209.7801   $209.78   $209.80   $209.80  
  Purchase #6 $211.66   6.134%   $224.6432   $224.64   $224.65   $224.60  
  Purchase #7 $134.82   4.827%   $141.3278   $141.33   $141.35   $141.30  
  7 purchase totals = $932.98       $995.5476   $995.55   $995.60   $995.50