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	$25.88	11.779%	$28.9284	$28.93	$28.95	$28.90
Purchase #2	$110.84	3.741%	$114.9865	$114.99	$115.00	$115.00
Purchase #3	$83.88	6.223%	$89.0999	$89.10	$89.10	$89.10
Purchase #4	$107.60	3.610%	$111.4844	$111.48	$111.50	$111.50
Purchase #5	$118.90	4.229%	$123.9283	$123.93	$123.95	$123.90
Purchase #6	$215.30	8.826%	$234.3024	$234.30	$234.30	$234.30
Purchase #7	$179.76	4.226%	$187.3567	$187.36	$187.35	$187.40
7 purchase totals =	$842.16		$890.0866	$890.09	$890.15	$890.10