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 $22.59   8.574%   $24.5269   $24.53   $24.55   $24.50  
  Purchase #2 $167.80   11.226%   $186.6372   $186.64   $186.65   $186.60  
  Purchase #3 $168.69   11.720%   $188.4605   $188.46   $188.45   $188.50  
  Purchase #4 $240.37   11.804%   $268.7433   $268.74   $268.75   $268.70  
  Purchase #5 $205.36   12.413%   $230.8513   $230.85   $230.85   $230.90  
  Purchase #6 $38.61   13.639%   $43.876   $43.88   $43.90   $43.90  
  Purchase #7 $21.30   12.378%   $23.9365   $23.94   $23.95   $23.90  
  7 purchase totals = $864.72       $967.0317   $967.04   $967.10   $967.00