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 $208.82   9.464%   $228.5827   $228.58   $228.60   $228.60  
  Purchase #2 $175.91   13.565%   $199.7722   $199.77   $199.75   $199.80  
  Purchase #3 $61.34   7.675%   $66.0478   $66.05   $66.05   $66.00  
  Purchase #4 $205.85   7.755%   $221.8137   $221.81   $221.80   $221.80  
  Purchase #5 $90.98   8.420%   $98.6405   $98.64   $98.65   $98.60  
  Purchase #6 $207.56   13.161%   $234.877   $234.88   $234.90   $234.90  
  Purchase #7 $49.48   6.319%   $52.6066   $52.61   $52.60   $52.60  
  7 purchase totals = $999.94       $1,102.3405   $1,102.34   $1,102.35   $1,102.30