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	$227.25	4.122%	$236.6172	$236.62	$236.60	$236.60
Purchase #2	$118.25	7.720%	$127.3789	$127.38	$127.40	$127.40
Purchase #3	$73.44	7.407%	$78.8797	$78.88	$78.90	$78.90
Purchase #4	$18.88	8.361%	$20.4586	$20.46	$20.45	$20.50
Purchase #5	$200.33	9.548%	$219.4575	$219.46	$219.45	$219.50
Purchase #6	$181.82	5.573%	$191.9528	$191.95	$191.95	$192.00
Purchase #7	$50.37	5.719%	$53.2507	$53.25	$53.25	$53.30
7 purchase totals =	$870.34		$927.9954	$928.00	$928.00	$928.20