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	$117.32	11.747%	$131.1016	$131.10	$131.10	$131.10
Purchase #2	$178.28	4.118%	$185.6216	$185.62	$185.60	$185.60
Purchase #3	$25.50	11.492%	$28.4305	$28.43	$28.45	$28.40
Purchase #4	$138.54	9.532%	$151.7456	$151.75	$151.75	$151.70
Purchase #5	$83.27	8.864%	$90.6511	$90.65	$90.65	$90.70
Purchase #6	$27.32	6.123%	$28.9928	$28.99	$29.00	$29.00
Purchase #7	$158.25	8.458%	$171.6348	$171.63	$171.65	$171.60
7 purchase totals =	$728.48		$788.1780	$788.17	$788.20	$788.10