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 $54.93   10.404%   $60.6449   $60.64   $60.65   $60.60  
  Purchase #2 $159.65   11.334%   $177.7447   $177.74   $177.75   $177.70  
  Purchase #3 $65.46   12.712%   $73.7813   $73.78   $73.80   $73.80  
  Purchase #4 $89.98   6.623%   $95.9394   $95.94   $95.95   $95.90  
  Purchase #5 $53.99   13.422%   $61.2365   $61.24   $61.25   $61.20  
  Purchase #6 $192.56   12.846%   $217.2963   $217.30   $217.30   $217.30  
  Purchase #7 $164.75   8.693%   $179.0717   $179.07   $179.05   $179.10  
  7 purchase totals = $781.32       $865.7148   $865.71   $865.75   $865.60