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	$145.99	9.497%	$159.8547	$159.85	$159.85	$159.90
Purchase #2	$123.43	6.557%	$131.5233	$131.52	$131.50	$131.50
Purchase #3	$40.86	11.232%	$45.4494	$45.45	$45.45	$45.40
Purchase #4	$19.70	4.178%	$20.5231	$20.52	$20.50	$20.50
Purchase #5	$98.91	11.689%	$110.4716	$110.47	$110.45	$110.50
Purchase #6	$23.75	13.195%	$26.8838	$26.88	$26.90	$26.90
Purchase #7	$206.86	10.284%	$228.1335	$228.13	$228.15	$228.10
7 purchase totals =	$659.50		$722.8394	$722.82	$722.80	$722.80