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	$53.70	5.612%	$56.7136	$56.71	$56.70	$56.70
Purchase #2	$118.33	11.259%	$131.6528	$131.65	$131.65	$131.70
Purchase #3	$29.73	11.145%	$33.0434	$33.04	$33.05	$33.00
Purchase #4	$114.45	7.592%	$123.139	$123.14	$123.15	$123.10
Purchase #5	$101.61	12.746%	$114.5612	$114.56	$114.55	$114.60
Purchase #6	$55.25	8.661%	$60.0352	$60.04	$60.05	$60.00
Purchase #7	$119.91	6.179%	$127.3192	$127.32	$127.30	$127.30
7 purchase totals =	$592.98		$646.4644	$646.46	$646.45	$646.40