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	$31.55	11.109%	$35.0549	$35.05	$35.05	$35.10
Purchase #2	$213.69	3.335%	$220.8166	$220.82	$220.80	$220.80
Purchase #3	$131.44	5.611%	$138.8151	$138.82	$138.80	$138.80
Purchase #4	$117.38	11.677%	$131.0865	$131.09	$131.10	$131.10
Purchase #5	$168.82	4.598%	$176.5823	$176.58	$176.60	$176.60
Purchase #6	$41.46	4.425%	$43.2946	$43.29	$43.30	$43.30
Purchase #7	$137.38	6.301%	$146.0363	$146.04	$146.05	$146.00
7 purchase totals =	$841.72		$891.6863	$891.69	$891.70	$891.70