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 $53.79   13.564%   $61.0861   $61.09   $61.10   $61.10  
  Purchase #2 $208.80   6.143%   $221.6266   $221.63   $221.65   $221.60  
  Purchase #3 $110.38   11.216%   $122.7602   $122.76   $122.75   $122.80  
  Purchase #4 $156.34   8.764%   $170.0416   $170.04   $170.05   $170.00  
  Purchase #5 $178.77   10.378%   $197.3228   $197.32   $197.30   $197.30  
  Purchase #6 $234.98   4.558%   $245.6904   $245.69   $245.70   $245.70  
  Purchase #7 $114.82   8.232%   $124.272   $124.27   $124.25   $124.30  
  7 purchase totals = $1,057.88       $1,142.7997   $1,142.80   $1,142.80   $1,142.80