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 $65.57   12.174%   $73.5525   $73.55   $73.55   $73.60  
  Purchase #2 $60.63   11.719%   $67.7352   $67.74   $67.75   $67.70  
  Purchase #3 $160.35   8.678%   $174.2652   $174.27   $174.25   $174.30  
  Purchase #4 $106.52   6.597%   $113.5471   $113.55   $113.55   $113.50  
  Purchase #5 $166.89   11.244%   $185.6551   $185.66   $185.65   $185.70  
  Purchase #6 $186.47   8.839%   $202.9521   $202.95   $202.95   $203.00  
  Purchase #7 $67.73   3.102%   $69.831   $69.83   $69.85   $69.80  
  7 purchase totals = $814.16       $887.5382   $887.55   $887.55   $887.60