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	$187.37	6.108%	$198.8146	$198.81	$198.80	$198.80
Purchase #2	$163.78	6.820%	$174.9498	$174.95	$174.95	$174.90
Purchase #3	$35.82	4.633%	$37.4795	$37.48	$37.50	$37.50
Purchase #4	$78.86	11.103%	$87.6158	$87.62	$87.60	$87.60
Purchase #5	$158.50	11.231%	$176.3011	$176.30	$176.30	$176.30
Purchase #6	$37.87	5.147%	$39.8192	$39.82	$39.80	$39.80
Purchase #7	$124.31	13.460%	$141.0421	$141.04	$141.05	$141.00
7 purchase totals =	$786.51		$856.0221	$856.02	$856.00	$855.90