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 $182.32   13.243%   $206.4646   $206.46   $206.45   $206.50  
  Purchase #2 $139.89   11.783%   $156.3732   $156.37   $156.35   $156.40  
  Purchase #3 $83.85   11.328%   $93.3485   $93.35   $93.35   $93.30  
  Purchase #4 $35.53   12.547%   $39.9879   $39.99   $40.00   $40.00  
  Purchase #5 $187.94   9.125%   $205.0895   $205.09   $205.10   $205.10  
  Purchase #6 $169.38   11.277%   $188.481   $188.48   $188.50   $188.50  
  Purchase #7 $88.56   4.438%   $92.4903   $92.49   $92.50   $92.50  
  7 purchase totals = $887.47       $982.2350   $982.23   $982.25   $982.30