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 $61.99   10.623%   $68.5752   $68.58   $68.60   $68.60  
  Purchase #2 $108.65   8.595%   $117.9885   $117.99   $118.00   $118.00  
  Purchase #3 $111.88   13.243%   $126.6963   $126.70   $126.70   $126.70  
  Purchase #4 $37.62   13.586%   $42.7311   $42.73   $42.75   $42.70  
  Purchase #5 $194.52   6.297%   $206.7689   $206.77   $206.75   $206.80  
  Purchase #6 $57.87   13.840%   $65.8792   $65.88   $65.90   $65.90  
  Purchase #7 $151.43   7.357%   $162.5707   $162.57   $162.55   $162.60  
  7 purchase totals = $723.96       $791.2099   $791.22   $791.25   $791.30