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	$64.42	13.493%	$73.1122	$73.11	$73.10	$73.10
Purchase #2	$56.37	9.557%	$61.7573	$61.76	$61.75	$61.80
Purchase #3	$225.61	10.126%	$248.4553	$248.46	$248.45	$248.50
Purchase #4	$27.83	12.693%	$31.3625	$31.36	$31.35	$31.40
Purchase #5	$13.49	11.582%	$15.0524	$15.05	$15.05	$15.10
Purchase #6	$111.80	6.729%	$119.323	$119.32	$119.30	$119.30
Purchase #7	$59.94	4.845%	$62.8441	$62.84	$62.85	$62.80
7 purchase totals =	$559.46		$611.9068	$611.90	$611.85	$612.00