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 $184.36   11.728%   $205.9817   $205.98   $206.00   $206.00  
  Purchase #2 $244.63   3.344%   $252.8104   $252.81   $252.80   $252.80  
  Purchase #3 $13.32   11.760%   $14.8864   $14.89   $14.90   $14.90  
  Purchase #4 $73.68   12.317%   $82.7552   $82.76   $82.75   $82.80  
  Purchase #5 $28.60   7.119%   $30.636   $30.64   $30.65   $30.60  
  Purchase #6 $10.54   11.652%   $11.7681   $11.77   $11.75   $11.80  
  Purchase #7 $20.46   6.542%   $21.7985   $21.80   $21.80   $21.80  
  7 purchase totals = $575.59       $620.6363   $620.65   $620.65   $620.70