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 $165.96   10.566%   $183.4953   $183.50   $183.50   $183.50  
  Purchase #2 $67.83   12.526%   $76.3264   $76.33   $76.35   $76.30  
  Purchase #3 $74.89   8.457%   $81.2234   $81.22   $81.20   $81.20  
  Purchase #4 $181.49   11.577%   $202.5011   $202.50   $202.50   $202.50  
  Purchase #5 $191.59   11.859%   $214.3107   $214.31   $214.30   $214.30  
  Purchase #6 $72.96   6.392%   $77.6236   $77.62   $77.60   $77.60  
  Purchase #7 $23.93   11.795%   $26.7525   $26.75   $26.75   $26.80  
  7 purchase totals = $778.65       $862.2330   $862.23   $862.20   $862.20