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 $153.47   9.663%   $168.2998   $168.30   $168.30   $168.30  
  Purchase #2 $123.34   10.695%   $136.5312   $136.53   $136.55   $136.50  
  Purchase #3 $235.67   6.608%   $251.2431   $251.24   $251.25   $251.20  
  Purchase #4 $93.89   3.621%   $97.2898   $97.29   $97.30   $97.30  
  Purchase #5 $28.49   7.530%   $30.6353   $30.64   $30.65   $30.60  
  Purchase #6 $238.97   4.730%   $250.2733   $250.27   $250.25   $250.30  
  Purchase #7 $47.36   3.458%   $48.9977   $49.00   $49.00   $49.00  
  7 purchase totals = $921.19       $983.2702   $983.27   $983.30   $983.20