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 $234.66   5.591%   $247.7798   $247.78   $247.80   $247.80  
  Purchase #2 $104.90   8.306%   $113.613   $113.61   $113.60   $113.60  
  Purchase #3 $60.77   8.748%   $66.0862   $66.09   $66.10   $66.10  
  Purchase #4 $7.33   3.458%   $7.5835   $7.58   $7.60   $7.60  
  Purchase #5 $159.80   10.542%   $176.6461   $176.65   $176.65   $176.60  
  Purchase #6 $166.36   5.588%   $175.6562   $175.66   $175.65   $175.70  
  Purchase #7 $222.63   9.104%   $242.8982   $242.90   $242.90   $242.90  
  7 purchase totals = $956.45       $1,030.2630   $1,030.27   $1,030.30   $1,030.30