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	$85.89	5.625%	$90.7213	$90.72	$90.70	$90.70
Purchase #2	$131.56	3.226%	$135.8041	$135.80	$135.80	$135.80
Purchase #3	$9.84	7.432%	$10.5713	$10.57	$10.55	$10.60
Purchase #4	$70.94	3.144%	$73.1704	$73.17	$73.15	$73.20
Purchase #5	$93.92	7.384%	$100.8551	$100.86	$100.85	$100.90
Purchase #6	$19.95	8.334%	$21.6126	$21.61	$21.60	$21.60
Purchase #7	$105.80	11.647%	$118.1225	$118.12	$118.10	$118.10
7 purchase totals =	$517.90		$550.8573	$550.85	$550.75	$550.90