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 $214.75   8.217%   $232.396   $232.40   $232.40   $232.40  
  Purchase #2 $119.40   5.832%   $126.3634   $126.36   $126.35   $126.40  
  Purchase #3 $21.78   13.125%   $24.6386   $24.64   $24.65   $24.60  
  Purchase #4 $138.97   11.714%   $155.2489   $155.25   $155.25   $155.20  
  Purchase #5 $162.69   7.781%   $175.3489   $175.35   $175.35   $175.30  
  Purchase #6 $174.88   13.311%   $198.1583   $198.16   $198.15   $198.20  
  Purchase #7 $44.32   4.628%   $46.3711   $46.37   $46.35   $46.40  
  7 purchase totals = $876.79       $958.5252   $958.53   $958.50   $958.50