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	$12.38	9.241%	$13.524	$13.52	$13.50	$13.50
Purchase #2	$56.34	10.539%	$62.2777	$62.28	$62.30	$62.30
Purchase #3	$165.28	9.128%	$180.3668	$180.37	$180.35	$180.40
Purchase #4	$38.39	6.269%	$40.7967	$40.80	$40.80	$40.80
Purchase #5	$177.74	9.377%	$194.4067	$194.41	$194.40	$194.40
Purchase #6	$206.36	9.221%	$225.3885	$225.39	$225.40	$225.40
Purchase #7	$39.97	4.713%	$41.8538	$41.85	$41.85	$41.90
7 purchase totals =	$696.46		$758.6142	$758.62	$758.60	$758.70