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	$185.77	10.201%	$204.7204	$204.72	$204.70	$204.70
Purchase #2	$206.78	10.774%	$229.0585	$229.06	$229.05	$229.10
Purchase #3	$42.57	9.321%	$46.5379	$46.54	$46.55	$46.50
Purchase #4	$86.28	3.656%	$89.4344	$89.43	$89.45	$89.40
Purchase #5	$10.54	3.630%	$10.9226	$10.92	$10.90	$10.90
Purchase #6	$60.62	10.654%	$67.0785	$67.08	$67.10	$67.10
Purchase #7	$11.65	10.260%	$12.8453	$12.85	$12.85	$12.80
7 purchase totals =	$604.21		$660.5976	$660.60	$660.60	$660.50