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 $92.83   13.195%   $105.0789   $105.08   $105.10   $105.10  
  Purchase #2 $25.39   7.543%   $27.3052   $27.31   $27.30   $27.30  
  Purchase #3 $52.37   9.706%   $57.453   $57.45   $57.45   $57.50  
  Purchase #4 $171.79   10.569%   $189.9465   $189.95   $189.95   $189.90  
  Purchase #5 $60.39   10.188%   $66.5425   $66.54   $66.55   $66.50  
  Purchase #6 $192.79   10.527%   $213.085   $213.09   $213.10   $213.10  
  Purchase #7 $194.66   3.797%   $202.0512   $202.05   $202.05   $202.10  
  7 purchase totals = $790.22       $861.4623   $861.47   $861.50   $861.50