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	$50.68	8.712%	$55.0952	$55.10	$55.10	$55.10
Purchase #2	$93.75	3.125%	$96.6797	$96.68	$96.70	$96.70
Purchase #3	$92.89	3.146%	$95.8123	$95.81	$95.80	$95.80
Purchase #4	$90.73	10.435%	$100.1977	$100.20	$100.20	$100.20
Purchase #5	$66.94	12.258%	$75.1455	$75.15	$75.15	$75.10
Purchase #6	$11.65	4.862%	$12.2164	$12.22	$12.20	$12.20
Purchase #7	$59.67	6.285%	$63.4203	$63.42	$63.40	$63.40
7 purchase totals =	$466.31		$498.5671	$498.58	$498.55	$498.50