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 $97.42   10.430%   $107.5809   $107.58   $107.60   $107.60  
  Purchase #2 $66.51   3.147%   $68.6031   $68.60   $68.60   $68.60  
  Purchase #3 $44.66   8.214%   $48.3284   $48.33   $48.35   $48.30  
  Purchase #4 $195.68   5.624%   $206.685   $206.69   $206.70   $206.70  
  Purchase #5 $228.99   8.290%   $247.9733   $247.97   $247.95   $248.00  
  Purchase #6 $225.98   7.292%   $242.4585   $242.46   $242.45   $242.50  
  Purchase #7 $64.44   12.646%   $72.5891   $72.59   $72.60   $72.60  
  7 purchase totals = $923.68       $994.2183   $994.22   $994.25   $994.30