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 $234.71   11.862%   $262.5513   $262.55   $262.55   $262.60  
  Purchase #2 $112.69   3.462%   $116.5913   $116.59   $116.60   $116.60  
  Purchase #3 $98.49   11.378%   $109.6962   $109.70   $109.70   $109.70  
  Purchase #4 $60.70   13.413%   $68.8417   $68.84   $68.85   $68.80  
  Purchase #5 $31.81   5.798%   $33.6543   $33.65   $33.65   $33.70  
  Purchase #6 $56.27   13.332%   $63.7719   $63.77   $63.75   $63.80  
  Purchase #7 $115.42   12.163%   $129.4585   $129.46   $129.45   $129.50  
  7 purchase totals = $710.09       $784.5652   $784.56   $784.55   $784.70