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 $46.62   13.129%   $52.7407   $52.74   $52.75   $52.70  
  Purchase #2 $169.76   11.682%   $189.5914   $189.59   $189.60   $189.60  
  Purchase #3 $208.36   9.412%   $227.9708   $227.97   $227.95   $228.00  
  Purchase #4 $239.71   7.217%   $257.0099   $257.01   $257.00   $257.00  
  Purchase #5 $82.70   5.493%   $87.2427   $87.24   $87.25   $87.20  
  Purchase #6 $11.61   7.604%   $12.4928   $12.49   $12.50   $12.50  
  Purchase #7 $18.87   6.151%   $20.0307   $20.03   $20.05   $20.00  
  7 purchase totals = $777.63       $847.0790   $847.07   $847.10   $847.00