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	$111.91	9.108%	$122.1028	$122.10	$122.10	$122.10
Purchase #2	$35.44	4.729%	$37.116	$37.12	$37.10	$37.10
Purchase #3	$130.68	10.167%	$143.9662	$143.97	$143.95	$144.00
Purchase #4	$89.63	5.473%	$94.5354	$94.54	$94.55	$94.50
Purchase #5	$101.55	9.776%	$111.4775	$111.48	$111.50	$111.50
Purchase #6	$64.30	6.216%	$68.2969	$68.30	$68.30	$68.30
Purchase #7	$20.80	3.291%	$21.4845	$21.48	$21.50	$21.50
7 purchase totals =	$554.31		$598.9793	$598.99	$599.00	$599.00