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	$56.92	10.250%	$62.7543	$62.75	$62.75	$62.80
Purchase #2	$139.40	13.193%	$157.791	$157.79	$157.80	$157.80
Purchase #3	$24.51	7.328%	$26.3061	$26.31	$26.30	$26.30
Purchase #4	$119.42	3.188%	$123.2271	$123.23	$123.25	$123.20
Purchase #5	$84.47	5.492%	$89.1091	$89.11	$89.10	$89.10
Purchase #6	$22.92	4.245%	$23.893	$23.89	$23.90	$23.90
Purchase #7	$145.61	7.354%	$156.3182	$156.32	$156.30	$156.30
7 purchase totals =	$593.25		$639.3988	$639.40	$639.40	$639.40