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	$159.96	3.722%	$165.9137	$165.91	$165.90	$165.90
Purchase #2	$171.61	8.287%	$185.8313	$185.83	$185.85	$185.80
Purchase #3	$67.32	7.604%	$72.439	$72.44	$72.45	$72.40
Purchase #4	$197.85	12.575%	$222.7296	$222.73	$222.75	$222.70
Purchase #5	$19.78	9.608%	$21.6805	$21.68	$21.70	$21.70
Purchase #6	$129.58	8.313%	$140.352	$140.35	$140.35	$140.40
Purchase #7	$49.85	4.575%	$52.1306	$52.13	$52.15	$52.10
7 purchase totals =	$795.95		$861.0767	$861.07	$861.15	$861.00