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 $177.37   7.663%   $190.9619   $190.96   $190.95   $191.00  
  Purchase #2 $192.95   4.589%   $201.8045   $201.80   $201.80   $201.80  
  Purchase #3 $216.96   10.285%   $239.2743   $239.27   $239.25   $239.30  
  Purchase #4 $239.65   11.431%   $267.0444   $267.04   $267.05   $267.00  
  Purchase #5 $209.55   13.159%   $237.1247   $237.12   $237.10   $237.10  
  Purchase #6 $134.60   8.814%   $146.4636   $146.46   $146.45   $146.50  
  Purchase #7 $114.44   11.771%   $127.9107   $127.91   $127.90   $127.90  
  7 purchase totals = $1,285.52       $1,410.5841   $1,410.56   $1,410.50   $1,410.60