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	$139.81	3.212%	$144.3007	$144.30	$144.30	$144.30
Purchase #2	$80.89	11.151%	$89.91	$89.91	$89.90	$89.90
Purchase #3	$179.45	6.187%	$190.5526	$190.55	$190.55	$190.60
Purchase #4	$44.60	9.367%	$48.7777	$48.78	$48.80	$48.80
Purchase #5	$56.93	4.633%	$59.5676	$59.57	$59.55	$59.60
Purchase #6	$55.45	6.276%	$58.93	$58.93	$58.95	$58.90
Purchase #7	$219.95	6.216%	$233.6221	$233.62	$233.60	$233.60
7 purchase totals =	$777.08		$825.6607	$825.66	$825.65	$825.70