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 $177.86   8.687%   $193.3107   $193.31   $193.30   $193.30  
  Purchase #2 $143.77   10.382%   $158.6962   $158.70   $158.70   $158.70  
  Purchase #3 $188.25   13.671%   $213.9857   $213.99   $214.00   $214.00  
  Purchase #4 $150.53   7.568%   $161.9221   $161.92   $161.90   $161.90  
  Purchase #5 $143.47   6.633%   $152.9864   $152.99   $153.00   $153.00  
  Purchase #6 $225.85   11.870%   $252.6584   $252.66   $252.65   $252.70  
  Purchase #7 $65.37   10.521%   $72.2476   $72.25   $72.25   $72.20  
  7 purchase totals = $1,095.10       $1,205.8071   $1,205.82   $1,205.80   $1,205.80