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 $61.70   6.224%   $65.5402   $65.54   $65.55   $65.50  
  Purchase #2 $68.55   7.239%   $73.5123   $73.51   $73.50   $73.50  
  Purchase #3 $162.40   9.599%   $177.9888   $177.99   $178.00   $178.00  
  Purchase #4 $167.55   13.406%   $190.0118   $190.01   $190.00   $190.00  
  Purchase #5 $215.36   7.705%   $231.9535   $231.95   $231.95   $232.00  
  Purchase #6 $38.64   9.345%   $42.2509   $42.25   $42.25   $42.30  
  Purchase #7 $47.76   7.789%   $51.48   $51.48   $51.50   $51.50  
  7 purchase totals = $761.96       $832.7375   $832.73   $832.75   $832.80