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	$19.69	8.506%	$21.3648	$21.36	$21.35	$21.40
Purchase #2	$147.67	13.793%	$168.0381	$168.04	$168.05	$168.00
Purchase #3	$115.27	7.548%	$123.9706	$123.97	$123.95	$124.00
Purchase #4	$86.42	3.281%	$89.2554	$89.26	$89.25	$89.30
Purchase #5	$45.32	6.264%	$48.1588	$48.16	$48.15	$48.20
Purchase #6	$107.31	11.699%	$119.8642	$119.86	$119.85	$119.90
Purchase #7	$114.64	10.849%	$127.0773	$127.08	$127.10	$127.10
7 purchase totals =	$636.32		$697.7292	$697.73	$697.70	$697.90