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	$91.35	6.484%	$97.2731	$97.27	$97.25	$97.30
Purchase #2	$88.93	9.228%	$97.1365	$97.14	$97.15	$97.10
Purchase #3	$64.28	10.285%	$70.8912	$70.89	$70.90	$70.90
Purchase #4	$72.77	13.321%	$82.4637	$82.46	$82.45	$82.50
Purchase #5	$55.95	8.228%	$60.5536	$60.55	$60.55	$60.60
Purchase #6	$42.84	12.554%	$48.2181	$48.22	$48.20	$48.20
Purchase #7	$160.98	13.796%	$183.1888	$183.19	$183.20	$183.20
7 purchase totals =	$577.10		$639.7250	$639.72	$639.70	$639.80