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 $57.98   9.595%   $63.5432   $63.54   $63.55   $63.50  
  Purchase #2 $72.54   3.697%   $75.2218   $75.22   $75.20   $75.20  
  Purchase #3 $224.43   9.858%   $246.5543   $246.55   $246.55   $246.60  
  Purchase #4 $241.62   4.613%   $252.7659   $252.77   $252.75   $252.80  
  Purchase #5 $122.39   3.326%   $126.4607   $126.46   $126.45   $126.50  
  Purchase #6 $48.38   11.451%   $53.92   $53.92   $53.90   $53.90  
  Purchase #7 $107.41   8.455%   $116.4915   $116.49   $116.50   $116.50  
  7 purchase totals = $874.75       $934.9574   $934.95   $934.90   $935.00