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	$79.73	11.664%	$89.0297	$89.03	$89.05	$89.00
Purchase #2	$208.46	7.178%	$223.4233	$223.42	$223.40	$223.40
Purchase #3	$213.75	5.407%	$225.3075	$225.31	$225.30	$225.30
Purchase #4	$161.76	7.308%	$173.5814	$173.58	$173.60	$173.60
Purchase #5	$181.76	5.166%	$191.1497	$191.15	$191.15	$191.10
Purchase #6	$27.90	11.772%	$31.1844	$31.18	$31.20	$31.20
Purchase #7	$19.49	6.582%	$20.7728	$20.77	$20.75	$20.80
7 purchase totals =	$892.85		$954.4488	$954.44	$954.45	$954.40