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 $226.72   9.622%   $248.535   $248.54   $248.55   $248.50  
  Purchase #2 $53.35   3.416%   $55.1724   $55.17   $55.15   $55.20  
  Purchase #3 $116.43   8.346%   $126.1472   $126.15   $126.15   $126.10  
  Purchase #4 $165.54   13.716%   $188.2455   $188.25   $188.25   $188.20  
  Purchase #5 $160.36   13.600%   $182.169   $182.17   $182.15   $182.20  
  Purchase #6 $187.62   3.451%   $194.0948   $194.09   $194.10   $194.10  
  Purchase #7 $230.98   3.581%   $239.2514   $239.25   $239.25   $239.30  
  7 purchase totals = $1,141.00       $1,233.6153   $1,233.62   $1,233.60   $1,233.60