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 $61.58   8.615%   $66.8851   $66.89   $66.90   $66.90  
  Purchase #2 $205.99   6.494%   $219.367   $219.37   $219.35   $219.40  
  Purchase #3 $85.77   11.774%   $95.8686   $95.87   $95.85   $95.90  
  Purchase #4 $67.81   4.403%   $70.7957   $70.80   $70.80   $70.80  
  Purchase #5 $163.26   7.207%   $175.0261   $175.03   $175.05   $175.00  
  Purchase #6 $134.77   3.733%   $139.801   $139.80   $139.80   $139.80  
  Purchase #7 $238.44   9.175%   $260.3169   $260.32   $260.30   $260.30  
  7 purchase totals = $957.62       $1,028.0604   $1,028.08   $1,028.05   $1,028.10