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 $42.76   12.406%   $48.0648   $48.06   $48.05   $48.10  
  Purchase #2 $85.37   4.649%   $89.3389   $89.34   $89.35   $89.30  
  Purchase #3 $119.50   11.183%   $132.8637   $132.86   $132.85   $132.90  
  Purchase #4 $205.81   12.726%   $232.0014   $232.00   $232.00   $232.00  
  Purchase #5 $82.86   12.223%   $92.988   $92.99   $93.00   $93.00  
  Purchase #6 $161.90   9.381%   $177.0878   $177.09   $177.10   $177.10  
  Purchase #7 $138.35   6.507%   $147.3524   $147.35   $147.35   $147.40  
  7 purchase totals = $836.55       $919.6970   $919.69   $919.70   $919.80