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 $146.40   3.491%   $151.5108   $151.51   $151.50   $151.50  
  Purchase #2 $181.81   5.746%   $192.2568   $192.26   $192.25   $192.30  
  Purchase #3 $240.25   10.794%   $266.1826   $266.18   $266.20   $266.20  
  Purchase #4 $56.61   6.295%   $60.1736   $60.17   $60.15   $60.20  
  Purchase #5 $119.75   6.862%   $127.9672   $127.97   $127.95   $128.00  
  Purchase #6 $154.90   10.542%   $171.2296   $171.23   $171.25   $171.20  
  Purchase #7 $84.94   10.360%   $93.7398   $93.74   $93.75   $93.70  
  7 purchase totals = $984.66       $1,063.0604   $1,063.06   $1,063.05   $1,063.10