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	$164.77	7.750%	$177.5397	$177.54	$177.55	$177.50
Purchase #2	$51.95	4.542%	$54.3096	$54.31	$54.30	$54.30
Purchase #3	$43.93	3.486%	$45.4614	$45.46	$45.45	$45.50
Purchase #4	$175.83	11.265%	$195.6372	$195.64	$195.65	$195.60
Purchase #5	$7.30	11.728%	$8.1561	$8.16	$8.15	$8.20
Purchase #6	$87.69	3.596%	$90.8433	$90.84	$90.85	$90.80
Purchase #7	$74.49	5.705%	$78.7397	$78.74	$78.75	$78.70
7 purchase totals =	$605.96		$650.6870	$650.69	$650.70	$650.60