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 $169.52   4.722%   $177.5247   $177.52   $177.50   $177.50  
  Purchase #2 $142.32   3.255%   $146.9525   $146.95   $146.95   $147.00  
  Purchase #3 $167.34   13.411%   $189.782   $189.78   $189.80   $189.80  
  Purchase #4 $119.62   12.781%   $134.9086   $134.91   $134.90   $134.90  
  Purchase #5 $184.76   11.470%   $205.952   $205.95   $205.95   $206.00  
  Purchase #6 $130.83   6.291%   $139.0605   $139.06   $139.05   $139.10  
  Purchase #7 $247.28   10.573%   $273.4249   $273.42   $273.40   $273.40  
  7 purchase totals = $1,161.67       $1,267.6052   $1,267.59   $1,267.55   $1,267.70