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	$149.44	13.832%	$170.1105	$170.11	$170.10	$170.10
Purchase #2	$101.67	12.164%	$114.0371	$114.04	$114.05	$114.00
Purchase #3	$29.94	3.795%	$31.0762	$31.08	$31.10	$31.10
Purchase #4	$197.29	6.357%	$209.8317	$209.83	$209.85	$209.80
Purchase #5	$100.90	10.305%	$111.2977	$111.30	$111.30	$111.30
Purchase #6	$79.47	8.693%	$86.3783	$86.38	$86.40	$86.40
Purchase #7	$175.72	5.456%	$185.3073	$185.31	$185.30	$185.30
7 purchase totals =	$834.43		$908.0388	$908.05	$908.10	$908.00