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 $194.85   12.546%   $219.2959   $219.30   $219.30   $219.30  
  Purchase #2 $179.98   12.197%   $201.9322   $201.93   $201.95   $201.90  
  Purchase #3 $21.98   10.281%   $24.2398   $24.24   $24.25   $24.20  
  Purchase #4 $126.85   13.153%   $143.5346   $143.53   $143.55   $143.50  
  Purchase #5 $53.79   3.660%   $55.7587   $55.76   $55.75   $55.80  
  Purchase #6 $47.81   3.254%   $49.3657   $49.37   $49.35   $49.40  
  Purchase #7 $235.28   8.420%   $255.0906   $255.09   $255.10   $255.10  
  7 purchase totals = $860.54       $949.2175   $949.22   $949.25   $949.20