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	$238.42	13.158%	$269.7913	$269.79	$269.80	$269.80
Purchase #2	$43.69	3.641%	$45.2808	$45.28	$45.30	$45.30
Purchase #3	$57.72	9.584%	$63.2519	$63.25	$63.25	$63.30
Purchase #4	$37.49	6.739%	$40.0165	$40.02	$40.00	$40.00
Purchase #5	$178.63	9.104%	$194.8925	$194.89	$194.90	$194.90
Purchase #6	$29.46	3.538%	$30.5023	$30.50	$30.50	$30.50
Purchase #7	$43.42	5.194%	$45.6752	$45.68	$45.70	$45.70
7 purchase totals =	$628.83		$689.4105	$689.41	$689.45	$689.50