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 $60.51   13.393%   $68.6141   $68.61   $68.60   $68.60  
  Purchase #2 $239.87   6.566%   $255.6199   $255.62   $255.60   $255.60  
  Purchase #3 $196.72   8.226%   $212.9022   $212.90   $212.90   $212.90  
  Purchase #4 $105.79   12.825%   $119.3576   $119.36   $119.35   $119.40  
  Purchase #5 $15.28   3.743%   $15.8519   $15.85   $15.85   $15.90  
  Purchase #6 $99.33   4.855%   $104.1525   $104.15   $104.15   $104.20  
  Purchase #7 $15.77   5.175%   $16.5861   $16.59   $16.60   $16.60  
  7 purchase totals = $733.27       $793.0843   $793.08   $793.05   $793.20