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	$51.79	9.131%	$56.5189	$56.52	$56.50	$56.50
Purchase #2	$19.91	6.216%	$21.1476	$21.15	$21.15	$21.10
Purchase #3	$9.49	6.219%	$10.0802	$10.08	$10.10	$10.10
Purchase #4	$228.59	3.475%	$236.5335	$236.53	$236.55	$236.50
Purchase #5	$209.99	6.488%	$223.6142	$223.61	$223.60	$223.60
Purchase #6	$99.91	3.728%	$103.6346	$103.63	$103.65	$103.60
Purchase #7	$158.73	8.809%	$172.7125	$172.71	$172.70	$172.70
7 purchase totals =	$778.41		$824.2415	$824.23	$824.25	$824.10