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	$64.64	10.446%	$71.3923	$71.39	$71.40	$71.40
Purchase #2	$202.94	8.432%	$220.0519	$220.05	$220.05	$220.10
Purchase #3	$78.83	5.298%	$83.0064	$83.01	$83.00	$83.00
Purchase #4	$137.57	9.260%	$150.309	$150.31	$150.30	$150.30
Purchase #5	$51.70	10.498%	$57.1275	$57.13	$57.15	$57.10
Purchase #6	$62.76	12.233%	$70.4374	$70.44	$70.45	$70.40
Purchase #7	$71.45	8.151%	$77.2739	$77.27	$77.25	$77.30
7 purchase totals =	$669.89		$729.5984	$729.60	$729.60	$729.60