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	$81.31	10.662%	$89.9793	$89.98	$90.00	$90.00
Purchase #2	$215.66	11.216%	$239.8484	$239.85	$239.85	$239.80
Purchase #3	$28.36	13.873%	$32.2944	$32.29	$32.30	$32.30
Purchase #4	$159.81	7.337%	$171.5353	$171.54	$171.55	$171.50
Purchase #5	$32.47	9.644%	$35.6014	$35.60	$35.60	$35.60
Purchase #6	$48.83	8.236%	$52.8516	$52.85	$52.85	$52.90
Purchase #7	$128.75	11.336%	$143.3451	$143.35	$143.35	$143.30
7 purchase totals =	$695.19		$765.4555	$765.46	$765.50	$765.40