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 $166.34   9.616%   $182.3353   $182.34   $182.35   $182.30  
  Purchase #2 $5.44   9.229%   $5.9421   $5.94   $5.95   $5.90  
  Purchase #3 $11.95   6.513%   $12.7283   $12.73   $12.75   $12.70  
  Purchase #4 $51.74   12.591%   $58.2546   $58.25   $58.25   $58.30  
  Purchase #5 $236.97   11.647%   $264.5699   $264.57   $264.55   $264.60  
  Purchase #6 $119.45   9.623%   $130.9447   $130.94   $130.95   $130.90  
  Purchase #7 $67.73   3.693%   $70.2313   $70.23   $70.25   $70.20  
  7 purchase totals = $659.62       $725.0062   $725.00   $725.05   $724.90