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 $234.67   11.120%   $260.7653   $260.77   $260.75   $260.80  
  Purchase #2 $204.39   9.844%   $224.5102   $224.51   $224.50   $224.50  
  Purchase #3 $5.27   11.806%   $5.8922   $5.89   $5.90   $5.90  
  Purchase #4 $139.44   13.501%   $158.2658   $158.27   $158.25   $158.30  
  Purchase #5 $33.94   7.667%   $36.5422   $36.54   $36.55   $36.50  
  Purchase #6 $61.99   6.302%   $65.8966   $65.90   $65.90   $65.90  
  Purchase #7 $53.85   5.124%   $56.6093   $56.61   $56.60   $56.60  
  7 purchase totals = $733.55       $808.4816   $808.49   $808.45   $808.50