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 $71.60   10.678%   $79.2454   $79.25   $79.25   $79.20  
  Purchase #2 $209.27   9.745%   $229.6634   $229.66   $229.65   $229.70  
  Purchase #3 $85.62   8.794%   $93.1494   $93.15   $93.15   $93.10  
  Purchase #4 $58.41   3.614%   $60.5209   $60.52   $60.50   $60.50  
  Purchase #5 $238.70   8.617%   $259.2688   $259.27   $259.25   $259.30  
  Purchase #6 $65.36   10.407%   $72.162   $72.16   $72.15   $72.20  
  Purchase #7 $8.92   5.866%   $9.4432   $9.44   $9.45   $9.40  
  7 purchase totals = $737.88       $803.4531   $803.45   $803.40   $803.40