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	$242.47	9.864%	$266.3872	$266.39	$266.40	$266.40
Purchase #2	$199.77	13.704%	$227.1465	$227.15	$227.15	$227.10
Purchase #3	$215.49	4.682%	$225.5792	$225.58	$225.60	$225.60
Purchase #4	$184.31	5.461%	$194.3752	$194.38	$194.40	$194.40
Purchase #5	$39.40	8.414%	$42.7151	$42.72	$42.70	$42.70
Purchase #6	$69.30	4.418%	$72.3617	$72.36	$72.35	$72.40
Purchase #7	$119.62	13.786%	$136.1108	$136.11	$136.10	$136.10
7 purchase totals =	$1,070.36		$1,164.6757	$1,164.69	$1,164.70	$1,164.70