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	$77.78	10.783%	$86.167	$86.17	$86.15	$86.20
Purchase #2	$177.43	7.201%	$190.2067	$190.21	$190.20	$190.20
Purchase #3	$242.89	8.868%	$264.4295	$264.43	$264.45	$264.40
Purchase #4	$79.35	4.373%	$82.82	$82.82	$82.80	$82.80
Purchase #5	$56.56	10.159%	$62.3059	$62.31	$62.30	$62.30
Purchase #6	$30.53	12.166%	$34.2443	$34.24	$34.25	$34.20
Purchase #7	$82.74	10.109%	$91.1042	$91.10	$91.10	$91.10
7 purchase totals =	$747.28		$811.2776	$811.28	$811.25	$811.20