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 $228.53   5.746%   $241.6613   $241.66   $241.65   $241.70  
  Purchase #2 $13.63   4.553%   $14.2506   $14.25   $14.25   $14.30  
  Purchase #3 $132.86   11.665%   $148.3581   $148.36   $148.35   $148.40  
  Purchase #4 $40.71   13.473%   $46.1949   $46.19   $46.20   $46.20  
  Purchase #5 $79.83   3.598%   $82.7023   $82.70   $82.70   $82.70  
  Purchase #6 $152.26   5.116%   $160.0496   $160.05   $160.05   $160.00  
  Purchase #7 $129.52   5.313%   $136.4014   $136.40   $136.40   $136.40  
  7 purchase totals = $777.34       $829.6182   $829.61   $829.60   $829.70