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 $30.63   13.452%   $34.7503   $34.75   $34.75   $34.80  
  Purchase #2 $87.26   6.832%   $93.2216   $93.22   $93.20   $93.20  
  Purchase #3 $9.25   13.481%   $10.497   $10.50   $10.50   $10.50  
  Purchase #4 $198.63   7.264%   $213.0585   $213.06   $213.05   $213.10  
  Purchase #5 $63.65   13.495%   $72.2396   $72.24   $72.25   $72.20  
  Purchase #6 $23.53   5.447%   $24.8117   $24.81   $24.80   $24.80  
  Purchase #7 $24.89   11.293%   $27.7008   $27.70   $27.70   $27.70  
  7 purchase totals = $437.84       $476.2795   $476.28   $476.25   $476.30