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	$99.66	10.533%	$110.1572	$110.16	$110.15	$110.20
Purchase #2	$96.42	7.624%	$103.7711	$103.77	$103.75	$103.80
Purchase #3	$240.51	10.804%	$266.4947	$266.49	$266.50	$266.50
Purchase #4	$61.83	6.611%	$65.9176	$65.92	$65.90	$65.90
Purchase #5	$88.67	11.330%	$98.7163	$98.72	$98.70	$98.70
Purchase #6	$89.39	11.817%	$99.9532	$99.95	$99.95	$100.00
Purchase #7	$94.44	3.866%	$98.0911	$98.09	$98.10	$98.10
7 purchase totals =	$770.92		$843.1012	$843.10	$843.05	$843.20