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 $175.38   5.660%   $185.3065   $185.31   $185.30   $185.30  
  Purchase #2 $226.53   5.821%   $239.7163   $239.72   $239.70   $239.70  
  Purchase #3 $15.78   11.573%   $17.6062   $17.61   $17.60   $17.60  
  Purchase #4 $55.50   11.450%   $61.8548   $61.85   $61.85   $61.90  
  Purchase #5 $165.68   8.796%   $180.2532   $180.25   $180.25   $180.30  
  Purchase #6 $182.28   5.349%   $192.0302   $192.03   $192.05   $192.00  
  Purchase #7 $161.34   6.453%   $171.7513   $171.75   $171.75   $171.80  
  7 purchase totals = $982.49       $1,048.5185   $1,048.52   $1,048.50   $1,048.60