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 $97.85   3.490%   $101.265   $101.27   $101.25   $101.30  
  Purchase #2 $76.48   11.233%   $85.071   $85.07   $85.05   $85.10  
  Purchase #3 $168.83   13.336%   $191.3452   $191.35   $191.35   $191.30  
  Purchase #4 $163.29   3.391%   $168.8272   $168.83   $168.85   $168.80  
  Purchase #5 $76.91   5.370%   $81.0401   $81.04   $81.05   $81.00  
  Purchase #6 $69.80   6.774%   $74.5283   $74.53   $74.55   $74.50  
  Purchase #7 $118.88   5.295%   $125.1747   $125.17   $125.15   $125.20  
  7 purchase totals = $772.04       $827.2515   $827.26   $827.25   $827.20