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	$54.55	5.409%	$57.5006	$57.50	$57.50	$57.50
Purchase #2	$72.27	10.630%	$79.9523	$79.95	$79.95	$80.00
Purchase #3	$120.35	5.722%	$127.2364	$127.24	$127.25	$127.20
Purchase #4	$35.78	13.814%	$40.7226	$40.72	$40.70	$40.70
Purchase #5	$44.39	10.442%	$49.0252	$49.03	$49.05	$49.00
Purchase #6	$11.80	13.332%	$13.3732	$13.37	$13.35	$13.40
Purchase #7	$124.42	13.528%	$141.2515	$141.25	$141.25	$141.30
7 purchase totals =	$463.56		$509.0618	$509.06	$509.05	$509.10