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 $55.37   6.248%   $58.8295   $58.83   $58.85   $58.80  
  Purchase #2 $215.37   13.688%   $244.8498   $244.85   $244.85   $244.80  
  Purchase #3 $122.79   7.128%   $131.5425   $131.54   $131.55   $131.50  
  Purchase #4 $53.28   13.806%   $60.6358   $60.64   $60.65   $60.60  
  Purchase #5 $177.95   4.280%   $185.5663   $185.57   $185.55   $185.60  
  Purchase #6 $206.71   8.607%   $224.5015   $224.50   $224.50   $224.50  
  Purchase #7 $140.29   7.750%   $151.1625   $151.16   $151.15   $151.20  
  7 purchase totals = $971.76       $1,057.0879   $1,057.09   $1,057.10   $1,057.00