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 $61.33   8.461%   $66.5191   $66.52   $66.50   $66.50  
  Purchase #2 $157.97   8.649%   $171.6328   $171.63   $171.65   $171.60  
  Purchase #3 $73.77   12.280%   $82.829   $82.83   $82.85   $82.80  
  Purchase #4 $184.99   4.487%   $193.2905   $193.29   $193.30   $193.30  
  Purchase #5 $43.31   12.381%   $48.6722   $48.67   $48.65   $48.70  
  Purchase #6 $101.82   12.300%   $114.3439   $114.34   $114.35   $114.30  
  Purchase #7 $239.68   13.227%   $271.3825   $271.38   $271.40   $271.40  
  7 purchase totals = $862.87       $948.6700   $948.66   $948.70   $948.60