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 $31.54   4.388%   $32.924   $32.92   $32.90   $32.90  
  Purchase #2 $65.80   9.303%   $71.9214   $71.92   $71.90   $71.90  
  Purchase #3 $58.94   4.535%   $61.6129   $61.61   $61.60   $61.60  
  Purchase #4 $46.28   5.729%   $48.9314   $48.93   $48.95   $48.90  
  Purchase #5 $213.77   7.108%   $228.9648   $228.96   $228.95   $229.00  
  Purchase #6 $18.58   5.202%   $19.5465   $19.55   $19.55   $19.50  
  Purchase #7 $50.54   9.175%   $55.177   $55.18   $55.20   $55.20  
  7 purchase totals = $485.45       $519.0780   $519.07   $519.05   $519.00