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 $56.88   8.185%   $61.5356   $61.54   $61.55   $61.50  
  Purchase #2 $102.78   13.509%   $116.6646   $116.66   $116.65   $116.70  
  Purchase #3 $199.58   12.135%   $223.799   $223.80   $223.80   $223.80  
  Purchase #4 $226.51   12.487%   $254.7943   $254.79   $254.80   $254.80  
  Purchase #5 $176.97   4.575%   $185.0664   $185.07   $185.05   $185.10  
  Purchase #6 $123.67   13.246%   $140.0513   $140.05   $140.05   $140.10  
  Purchase #7 $178.36   3.213%   $184.0907   $184.09   $184.10   $184.10  
  7 purchase totals = $1,064.75       $1,166.0019   $1,166.00   $1,166.00   $1,166.10