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	$243.83	4.781%	$255.4875	$255.49	$255.50	$255.50
Purchase #2	$52.67	12.148%	$59.0684	$59.07	$59.05	$59.10
Purchase #3	$103.50	7.279%	$111.0338	$111.03	$111.05	$111.00
Purchase #4	$163.68	12.478%	$184.104	$184.10	$184.10	$184.10
Purchase #5	$9.65	9.861%	$10.6016	$10.60	$10.60	$10.60
Purchase #6	$107.98	4.535%	$112.8769	$112.88	$112.90	$112.90
Purchase #7	$23.80	5.428%	$25.0919	$25.09	$25.10	$25.10
7 purchase totals =	$705.11		$758.2641	$758.26	$758.30	$758.30