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	$150.72	5.566%	$159.1091	$159.11	$159.10	$159.10
Purchase #2	$120.67	6.196%	$128.1467	$128.15	$128.15	$128.10
Purchase #3	$92.79	8.179%	$100.3793	$100.38	$100.40	$100.40
Purchase #4	$21.62	12.106%	$24.2373	$24.24	$24.25	$24.20
Purchase #5	$184.57	3.533%	$191.0909	$191.09	$191.10	$191.10
Purchase #6	$54.58	3.721%	$56.6109	$56.61	$56.60	$56.60
Purchase #7	$104.93	4.838%	$110.0065	$110.01	$110.00	$110.00
7 purchase totals =	$729.88		$769.5807	$769.59	$769.60	$769.50