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	$122.33	6.455%	$130.2264	$130.23	$130.25	$130.20
Purchase #2	$158.93	5.423%	$167.5488	$167.55	$167.55	$167.50
Purchase #3	$128.46	8.314%	$139.1402	$139.14	$139.15	$139.10
Purchase #4	$44.71	3.232%	$46.155	$46.16	$46.15	$46.20
Purchase #5	$52.83	12.664%	$59.5204	$59.52	$59.50	$59.50
Purchase #6	$123.85	3.125%	$127.7203	$127.72	$127.70	$127.70
Purchase #7	$94.84	7.627%	$102.0734	$102.07	$102.05	$102.10
7 purchase totals =	$725.95		$772.3845	$772.39	$772.35	$772.30