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	$19.54	9.804%	$21.4557	$21.46	$21.45	$21.50
Purchase #2	$73.96	3.411%	$76.4828	$76.48	$76.50	$76.50
Purchase #3	$231.57	7.124%	$248.067	$248.07	$248.05	$248.10
Purchase #4	$37.98	12.831%	$42.8532	$42.85	$42.85	$42.90
Purchase #5	$225.77	12.214%	$253.3455	$253.35	$253.35	$253.30
Purchase #6	$111.34	4.844%	$116.7333	$116.73	$116.75	$116.70
Purchase #7	$56.28	6.419%	$59.8926	$59.89	$59.90	$59.90
7 purchase totals =	$756.44		$818.8301	$818.83	$818.85	$818.90