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 $144.89   11.835%   $162.0377   $162.04   $162.05   $162.00  
  Purchase #2 $68.49   12.295%   $76.9108   $76.91   $76.90   $76.90  
  Purchase #3 $138.53   13.444%   $157.154   $157.15   $157.15   $157.20  
  Purchase #4 $26.32   9.239%   $28.7517   $28.75   $28.75   $28.80  
  Purchase #5 $124.68   4.493%   $130.2819   $130.28   $130.30   $130.30  
  Purchase #6 $105.62   6.451%   $112.4335   $112.43   $112.45   $112.40  
  Purchase #7 $149.50   6.110%   $158.6345   $158.63   $158.65   $158.60  
  7 purchase totals = $758.03       $826.2041   $826.19   $826.25   $826.20