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 $41.38   4.383%   $43.1937   $43.19   $43.20   $43.20  
  Purchase #2 $189.33   11.713%   $211.5062   $211.51   $211.50   $211.50  
  Purchase #3 $44.85   6.351%   $47.6984   $47.70   $47.70   $47.70  
  Purchase #4 $146.31   10.632%   $161.8657   $161.87   $161.85   $161.90  
  Purchase #5 $68.32   9.243%   $74.6348   $74.63   $74.65   $74.60  
  Purchase #6 $55.99   9.351%   $61.2256   $61.23   $61.25   $61.20  
  Purchase #7 $220.93   6.792%   $235.9356   $235.94   $235.95   $235.90  
  7 purchase totals = $767.11       $836.0600   $836.07   $836.10   $836.00