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	$79.82	12.477%	$89.7791	$89.78	$89.80	$89.80
Purchase #2	$211.67	6.708%	$225.8688	$225.87	$225.85	$225.90
Purchase #3	$139.61	8.581%	$151.5899	$151.59	$151.60	$151.60
Purchase #4	$89.55	11.775%	$100.0945	$100.09	$100.10	$100.10
Purchase #5	$179.46	12.648%	$202.1581	$202.16	$202.15	$202.20
Purchase #6	$32.99	8.248%	$35.711	$35.71	$35.70	$35.70
Purchase #7	$100.94	5.698%	$106.6916	$106.69	$106.70	$106.70
7 purchase totals =	$834.04		$911.8930	$911.89	$911.90	$912.00