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	$8.56	9.681%	$9.3887	$9.39	$9.40	$9.40
Purchase #2	$80.60	6.831%	$86.1058	$86.11	$86.10	$86.10
Purchase #3	$114.72	11.202%	$127.5709	$127.57	$127.55	$127.60
Purchase #4	$97.54	8.809%	$106.1323	$106.13	$106.15	$106.10
Purchase #5	$111.75	13.693%	$127.0519	$127.05	$127.05	$127.10
Purchase #6	$32.47	9.809%	$35.655	$35.66	$35.65	$35.70
Purchase #7	$150.29	10.810%	$166.5363	$166.54	$166.55	$166.50
7 purchase totals =	$595.93		$658.4409	$658.45	$658.45	$658.50