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 $249.63   10.654%   $276.2256   $276.23   $276.25   $276.20  
  Purchase #2 $13.59   5.596%   $14.3505   $14.35   $14.35   $14.40  
  Purchase #3 $21.73   3.700%   $22.534   $22.53   $22.55   $22.50  
  Purchase #4 $177.66   4.747%   $186.0935   $186.09   $186.10   $186.10  
  Purchase #5 $73.83   4.112%   $76.8659   $76.87   $76.85   $76.90  
  Purchase #6 $233.28   11.210%   $259.4307   $259.43   $259.45   $259.40  
  Purchase #7 $241.88   4.746%   $253.3596   $253.36   $253.35   $253.40  
  7 purchase totals = $1,011.60       $1,088.8598   $1,088.86   $1,088.90   $1,088.90