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 $224.42   10.847%   $248.7628   $248.76   $248.75   $248.80  
  Purchase #2 $80.65   13.856%   $91.8249   $91.82   $91.80   $91.80  
  Purchase #3 $206.69   12.688%   $232.9148   $232.91   $232.90   $232.90  
  Purchase #4 $79.67   5.586%   $84.1204   $84.12   $84.10   $84.10  
  Purchase #5 $46.32   11.235%   $51.5241   $51.52   $51.50   $51.50  
  Purchase #6 $85.55   10.422%   $94.466   $94.47   $94.45   $94.50  
  Purchase #7 $46.87   13.167%   $53.0414   $53.04   $53.05   $53.00  
  7 purchase totals = $770.17       $856.6544   $856.64   $856.55   $856.60