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 $31.81   11.407%   $35.4386   $35.44   $35.45   $35.40  
  Purchase #2 $53.50   3.544%   $55.396   $55.40   $55.40   $55.40  
  Purchase #3 $76.98   9.324%   $84.1576   $84.16   $84.15   $84.20  
  Purchase #4 $52.26   12.132%   $58.6002   $58.60   $58.60   $58.60  
  Purchase #5 $103.71   7.670%   $111.6646   $111.66   $111.65   $111.70  
  Purchase #6 $177.78   6.263%   $188.9144   $188.91   $188.90   $188.90  
  Purchase #7 $236.53   9.275%   $258.4682   $258.47   $258.45   $258.50  
  7 purchase totals = $732.57       $792.6396   $792.64   $792.60   $792.70