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 $182.78   13.656%   $207.7404   $207.74   $207.75   $207.70  
  Purchase #2 $61.45   12.196%   $68.9444   $68.94   $68.95   $68.90  
  Purchase #3 $76.92   6.744%   $82.1075   $82.11   $82.10   $82.10  
  Purchase #4 $40.89   7.187%   $43.8288   $43.83   $43.85   $43.80  
  Purchase #5 $247.82   5.657%   $261.8392   $261.84   $261.85   $261.80  
  Purchase #6 $34.58   9.596%   $37.8983   $37.90   $37.90   $37.90  
  Purchase #7 $231.92   9.779%   $254.5995   $254.60   $254.60   $254.60  
  7 purchase totals = $876.36       $956.9581   $956.96   $957.00   $956.80