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 $60.70   13.524%   $68.9091   $68.91   $68.90   $68.90  
  Purchase #2 $163.78   9.148%   $178.7626   $178.76   $178.75   $178.80  
  Purchase #3 $29.99   10.863%   $33.2478   $33.25   $33.25   $33.20  
  Purchase #4 $98.38   5.705%   $103.9926   $103.99   $104.00   $104.00  
  Purchase #5 $32.76   5.778%   $34.6529   $34.65   $34.65   $34.70  
  Purchase #6 $246.72   11.461%   $274.9966   $275.00   $275.00   $275.00  
  Purchase #7 $44.83   9.178%   $48.9445   $48.94   $48.95   $48.90  
  7 purchase totals = $677.16       $743.5061   $743.50   $743.50   $743.50