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	$138.57	3.275%	$143.1082	$143.11	$143.10	$143.10
Purchase #2	$186.93	12.212%	$209.7579	$209.76	$209.75	$209.80
Purchase #3	$47.99	13.757%	$54.592	$54.59	$54.60	$54.60
Purchase #4	$215.36	3.227%	$222.3097	$222.31	$222.30	$222.30
Purchase #5	$92.54	9.510%	$101.3406	$101.34	$101.35	$101.30
Purchase #6	$10.48	8.623%	$11.3837	$11.38	$11.40	$11.40
Purchase #7	$114.65	3.763%	$118.9643	$118.96	$118.95	$119.00
7 purchase totals =	$806.52		$861.4564	$861.45	$861.45	$861.50