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	$78.60	13.407%	$89.1379	$89.14	$89.15	$89.10
Purchase #2	$172.60	13.411%	$195.7474	$195.75	$195.75	$195.70
Purchase #3	$46.52	13.587%	$52.8407	$52.84	$52.85	$52.80
Purchase #4	$167.41	10.811%	$185.5087	$185.51	$185.50	$185.50
Purchase #5	$79.97	4.159%	$83.296	$83.30	$83.30	$83.30
Purchase #6	$84.69	11.762%	$94.6512	$94.65	$94.65	$94.70
Purchase #7	$114.42	12.648%	$128.8918	$128.89	$128.90	$128.90
7 purchase totals =	$744.21		$830.0737	$830.08	$830.10	$830.00