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	$89.73	13.467%	$101.8139	$101.81	$101.80	$101.80
Purchase #2	$29.64	5.856%	$31.3757	$31.38	$31.40	$31.40
Purchase #3	$245.25	7.152%	$262.7903	$262.79	$262.80	$262.80
Purchase #4	$108.61	5.736%	$114.8399	$114.84	$114.85	$114.80
Purchase #5	$171.99	9.277%	$187.9455	$187.95	$187.95	$187.90
Purchase #6	$79.89	12.299%	$89.7157	$89.72	$89.70	$89.70
Purchase #7	$245.49	4.784%	$257.2342	$257.23	$257.25	$257.20
7 purchase totals =	$970.60		$1,045.7152	$1,045.72	$1,045.75	$1,045.60