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 $38.33   12.425%   $43.0925   $43.09   $43.10   $43.10  
  Purchase #2 $227.40   11.489%   $253.526   $253.53   $253.55   $253.50  
  Purchase #3 $33.40   7.356%   $35.8569   $35.86   $35.85   $35.90  
  Purchase #4 $222.78   7.502%   $239.493   $239.49   $239.50   $239.50  
  Purchase #5 $154.96   6.636%   $165.2431   $165.24   $165.25   $165.20  
  Purchase #6 $60.51   3.596%   $62.6859   $62.69   $62.70   $62.70  
  Purchase #7 $166.48   13.392%   $188.775   $188.78   $188.80   $188.80  
  7 purchase totals = $903.86       $988.6724   $988.68   $988.75   $988.70