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	$100.45	9.145%	$109.6362	$109.64	$109.65	$109.60
Purchase #2	$190.78	4.613%	$199.5807	$199.58	$199.60	$199.60
Purchase #3	$96.85	3.293%	$100.0393	$100.04	$100.05	$100.00
Purchase #4	$92.99	7.257%	$99.7383	$99.74	$99.75	$99.70
Purchase #5	$74.77	4.715%	$78.2954	$78.30	$78.30	$78.30
Purchase #6	$6.80	4.578%	$7.1113	$7.11	$7.10	$7.10
Purchase #7	$205.63	8.409%	$222.9214	$222.92	$222.90	$222.90
7 purchase totals =	$768.27		$817.3226	$817.33	$817.35	$817.20