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	$103.42	8.136%	$111.8343	$111.83	$111.85	$111.80
Purchase #2	$115.93	11.253%	$128.9756	$128.98	$129.00	$129.00
Purchase #3	$92.49	4.694%	$96.8315	$96.83	$96.85	$96.80
Purchase #4	$95.84	4.465%	$100.1193	$100.12	$100.10	$100.10
Purchase #5	$178.91	5.285%	$188.3654	$188.37	$188.35	$188.40
Purchase #6	$23.50	6.450%	$25.0158	$25.02	$25.00	$25.00
Purchase #7	$35.48	8.591%	$38.5281	$38.53	$38.55	$38.50
7 purchase totals =	$645.57		$689.6700	$689.68	$689.70	$689.60