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 $62.74   5.106%   $65.9435   $65.94   $65.95   $65.90  
  Purchase #2 $75.98   7.852%   $81.9459   $81.95   $81.95   $81.90  
  Purchase #3 $62.66   3.738%   $65.0022   $65.00   $65.00   $65.00  
  Purchase #4 $87.99   13.387%   $99.7692   $99.77   $99.75   $99.80  
  Purchase #5 $47.57   9.436%   $52.0587   $52.06   $52.05   $52.10  
  Purchase #6 $14.66   10.378%   $16.1814   $16.18   $16.20   $16.20  
  Purchase #7 $208.42   13.117%   $235.7585   $235.76   $235.75   $235.80  
  7 purchase totals = $560.02       $616.6594   $616.66   $616.65   $616.70