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 $30.84   9.465%   $33.759   $33.76   $33.75   $33.80  
  Purchase #2 $213.66   9.606%   $234.1842   $234.18   $234.20   $234.20  
  Purchase #3 $201.96   11.255%   $224.6906   $224.69   $224.70   $224.70  
  Purchase #4 $156.67   6.737%   $167.2249   $167.22   $167.20   $167.20  
  Purchase #5 $107.27   10.206%   $118.218   $118.22   $118.20   $118.20  
  Purchase #6 $230.61   9.467%   $252.4418   $252.44   $252.45   $252.40  
  Purchase #7 $118.53   11.637%   $132.3233   $132.32   $132.30   $132.30  
  7 purchase totals = $1,059.54       $1,162.8418   $1,162.83   $1,162.80   $1,162.80