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 $213.37   10.746%   $236.2987   $236.30   $236.30   $236.30  
  Purchase #2 $204.99   4.110%   $213.4151   $213.42   $213.40   $213.40  
  Purchase #3 $15.49   13.601%   $17.5968   $17.60   $17.60   $17.60  
  Purchase #4 $61.67   6.366%   $65.5959   $65.60   $65.60   $65.60  
  Purchase #5 $153.35   4.791%   $160.697   $160.70   $160.70   $160.70  
  Purchase #6 $112.37   13.357%   $127.3793   $127.38   $127.40   $127.40  
  Purchase #7 $186.74   4.614%   $195.3562   $195.36   $195.35   $195.40  
  7 purchase totals = $947.98       $1,016.3390   $1,016.36   $1,016.35   $1,016.40