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 $77.96   9.147%   $85.091   $85.09   $85.10   $85.10  
  Purchase #2 $232.68   13.417%   $263.8987   $263.90   $263.90   $263.90  
  Purchase #3 $176.92   3.423%   $182.976   $182.98   $183.00   $183.00  
  Purchase #4 $201.46   5.724%   $212.9916   $212.99   $213.00   $213.00  
  Purchase #5 $52.78   8.428%   $57.2283   $57.23   $57.25   $57.20  
  Purchase #6 $60.90   7.129%   $65.2416   $65.24   $65.25   $65.20  
  Purchase #7 $174.87   3.215%   $180.4921   $180.49   $180.50   $180.50  
  7 purchase totals = $977.57       $1,047.9193   $1,047.92   $1,048.00   $1,047.90