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	$91.80	13.552%	$104.2407	$104.24	$104.25	$104.20
Purchase #2	$97.92	11.543%	$109.2229	$109.22	$109.20	$109.20
Purchase #3	$115.60	11.265%	$128.6223	$128.62	$128.60	$128.60
Purchase #4	$235.74	8.292%	$255.2876	$255.29	$255.30	$255.30
Purchase #5	$183.27	9.346%	$200.3984	$200.40	$200.40	$200.40
Purchase #6	$104.54	4.867%	$109.628	$109.63	$109.65	$109.60
Purchase #7	$245.28	13.757%	$279.0232	$279.02	$279.00	$279.00
7 purchase totals =	$1,074.15		$1,186.4231	$1,186.42	$1,186.40	$1,186.30