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	$171.38	11.203%	$190.5797	$190.58	$190.60	$190.60
Purchase #2	$93.92	10.854%	$104.1141	$104.11	$104.10	$104.10
Purchase #3	$149.72	12.677%	$168.7	$168.70	$168.70	$168.70
Purchase #4	$114.67	11.155%	$127.4614	$127.46	$127.45	$127.50
Purchase #5	$109.75	12.434%	$123.3963	$123.40	$123.40	$123.40
Purchase #6	$9.62	10.670%	$10.6465	$10.65	$10.65	$10.60
Purchase #7	$69.74	13.106%	$78.8801	$78.88	$78.90	$78.90
7 purchase totals =	$718.80		$803.7781	$803.78	$803.80	$803.80