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 $30.26   12.432%   $34.0219   $34.02   $34.00   $34.00  
  Purchase #2 $88.97   11.212%   $98.9453   $98.95   $98.95   $98.90  
  Purchase #3 $53.63   12.629%   $60.4029   $60.40   $60.40   $60.40  
  Purchase #4 $18.96   11.471%   $21.1349   $21.13   $21.15   $21.10  
  Purchase #5 $25.68   10.711%   $28.4306   $28.43   $28.45   $28.40  
  Purchase #6 $61.54   6.277%   $65.4029   $65.40   $65.40   $65.40  
  Purchase #7 $69.81   9.186%   $76.2227   $76.22   $76.20   $76.20  
  7 purchase totals = $348.85       $384.5612   $384.55   $384.55   $384.40