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	$178.82	3.508%	$185.093	$185.09	$185.10	$185.10
Purchase #2	$6.66	10.863%	$7.3835	$7.38	$7.40	$7.40
Purchase #3	$97.58	7.607%	$105.0029	$105.00	$105.00	$105.00
Purchase #4	$78.50	7.556%	$84.4315	$84.43	$84.45	$84.40
Purchase #5	$133.89	4.235%	$139.5602	$139.56	$139.55	$139.60
Purchase #6	$31.95	12.481%	$35.9377	$35.94	$35.95	$35.90
Purchase #7	$25.80	6.641%	$27.5134	$27.51	$27.50	$27.50
7 purchase totals =	$553.20		$584.9222	$584.91	$584.95	$584.90