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 $173.83   12.843%   $196.155   $196.16   $196.15   $196.20  
  Purchase #2 $30.89   4.337%   $32.2297   $32.23   $32.25   $32.20  
  Purchase #3 $86.58   8.805%   $94.2034   $94.20   $94.20   $94.20  
  Purchase #4 $7.59   5.145%   $7.9805   $7.98   $8.00   $8.00  
  Purchase #5 $77.67   8.515%   $84.2836   $84.28   $84.30   $84.30  
  Purchase #6 $250.91   9.396%   $274.4855   $274.49   $274.50   $274.50  
  Purchase #7 $33.47   12.528%   $37.6631   $37.66   $37.65   $37.70  
  7 purchase totals = $660.94       $727.0008   $727.00   $727.05   $727.10