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 $217.50   7.131%   $233.0099   $233.01   $233.00   $233.00  
  Purchase #2 $119.49   12.605%   $134.5517   $134.55   $134.55   $134.60  
  Purchase #3 $89.39   5.122%   $93.9686   $93.97   $93.95   $94.00  
  Purchase #4 $50.59   8.381%   $54.8299   $54.83   $54.85   $54.80  
  Purchase #5 $215.32   9.186%   $235.0993   $235.10   $235.10   $235.10  
  Purchase #6 $167.86   5.678%   $177.3911   $177.39   $177.40   $177.40  
  Purchase #7 $112.44   9.173%   $122.7541   $122.75   $122.75   $122.80  
  7 purchase totals = $972.59       $1,051.6046   $1,051.60   $1,051.60   $1,051.70