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 $99.55   6.125%   $105.6474   $105.65   $105.65   $105.60  
  Purchase #2 $18.74   13.270%   $21.2268   $21.23   $21.25   $21.20  
  Purchase #3 $6.64   9.126%   $7.246   $7.25   $7.25   $7.20  
  Purchase #4 $193.44   3.722%   $200.6398   $200.64   $200.65   $200.60  
  Purchase #5 $8.51   12.176%   $9.5462   $9.55   $9.55   $9.50  
  Purchase #6 $102.98   13.509%   $116.8916   $116.89   $116.90   $116.90  
  Purchase #7 $28.53   8.759%   $31.0289   $31.03   $31.05   $31.00  
  7 purchase totals = $458.39       $492.2267   $492.24   $492.30   $492.00