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 $97.27   6.667%   $103.755   $103.76   $103.75   $103.80  
  Purchase #2 $14.44   10.440%   $15.9475   $15.95   $15.95   $15.90  
  Purchase #3 $201.60   11.186%   $224.151   $224.15   $224.15   $224.20  
  Purchase #4 $60.66   8.398%   $65.7542   $65.75   $65.75   $65.80  
  Purchase #5 $12.97   4.106%   $13.5025   $13.50   $13.50   $13.50  
  Purchase #6 $34.27   3.621%   $35.5109   $35.51   $35.50   $35.50  
  Purchase #7 $229.94   12.237%   $258.0778   $258.08   $258.10   $258.10  
  7 purchase totals = $651.15       $716.6989   $716.70   $716.70   $716.80