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	$34.42	13.787%	$39.1655	$39.17	$39.15	$39.20
Purchase #2	$205.71	7.104%	$220.3236	$220.32	$220.30	$220.30
Purchase #3	$235.71	13.158%	$266.7247	$266.72	$266.70	$266.70
Purchase #4	$66.87	6.596%	$71.2807	$71.28	$71.30	$71.30
Purchase #5	$119.80	6.120%	$127.1318	$127.13	$127.15	$127.10
Purchase #6	$230.59	11.475%	$257.0502	$257.05	$257.05	$257.10
Purchase #7	$29.73	12.144%	$33.3404	$33.34	$33.35	$33.30
7 purchase totals =	$922.83		$1,015.0169	$1,015.01	$1,015.00	$1,015.00