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 $164.62   11.165%   $182.9998   $183.00   $183.00   $183.00  
  Purchase #2 $17.94   6.124%   $19.0386   $19.04   $19.05   $19.00  
  Purchase #3 $41.69   6.149%   $44.2535   $44.25   $44.25   $44.30  
  Purchase #4 $113.81   10.538%   $125.8033   $125.80   $125.80   $125.80  
  Purchase #5 $123.35   11.407%   $137.4205   $137.42   $137.40   $137.40  
  Purchase #6 $185.65   5.742%   $196.31   $196.31   $196.30   $196.30  
  Purchase #7 $133.49   11.259%   $148.5196   $148.52   $148.50   $148.50  
  7 purchase totals = $780.55       $854.3453   $854.34   $854.30   $854.30