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 $241.41   11.417%   $268.9718   $268.97   $268.95   $269.00  
  Purchase #2 $243.26   9.449%   $266.2456   $266.25   $266.25   $266.20  
  Purchase #3 $31.95   5.126%   $33.5878   $33.59   $33.60   $33.60  
  Purchase #4 $150.77   7.745%   $162.4471   $162.45   $162.45   $162.40  
  Purchase #5 $173.56   8.815%   $188.8593   $188.86   $188.85   $188.90  
  Purchase #6 $114.69   9.665%   $125.7748   $125.77   $125.75   $125.80  
  Purchase #7 $70.76   11.584%   $78.9568   $78.96   $78.95   $79.00  
  7 purchase totals = $1,026.40       $1,124.8432   $1,124.85   $1,124.80   $1,124.90