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 $162.61   13.567%   $184.6713   $184.67   $184.65   $184.70  
  Purchase #2 $93.49   3.372%   $96.6425   $96.64   $96.65   $96.60  
  Purchase #3 $207.65   5.857%   $219.8121   $219.81   $219.80   $219.80  
  Purchase #4 $17.87   3.743%   $18.5389   $18.54   $18.55   $18.50  
  Purchase #5 $21.37   6.467%   $22.752   $22.75   $22.75   $22.80  
  Purchase #6 $36.50   5.768%   $38.6053   $38.61   $38.60   $38.60  
  Purchase #7 $40.33   8.547%   $43.777   $43.78   $43.80   $43.80  
  7 purchase totals = $579.82       $624.7991   $624.80   $624.80   $624.80