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 $96.86   11.596%   $108.0919   $108.09   $108.10   $108.10  
  Purchase #2 $128.86   9.133%   $140.6288   $140.63   $140.65   $140.60  
  Purchase #3 $17.87   5.777%   $18.9023   $18.90   $18.90   $18.90  
  Purchase #4 $83.29   10.109%   $91.7098   $91.71   $91.70   $91.70  
  Purchase #5 $61.25   13.468%   $69.4992   $69.50   $69.50   $69.50  
  Purchase #6 $154.90   13.748%   $176.1957   $176.20   $176.20   $176.20  
  Purchase #7 $244.66   10.256%   $269.7523   $269.75   $269.75   $269.80  
  7 purchase totals = $787.69       $874.7800   $874.78   $874.80   $874.80