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	$31.71	3.745%	$32.8975	$32.90	$32.90	$32.90
Purchase #2	$123.93	11.808%	$138.5637	$138.56	$138.55	$138.60
Purchase #3	$51.72	3.293%	$53.4231	$53.42	$53.40	$53.40
Purchase #4	$234.28	10.432%	$258.7201	$258.72	$258.70	$258.70
Purchase #5	$202.68	12.160%	$227.3259	$227.33	$227.35	$227.30
Purchase #6	$109.64	12.433%	$123.2715	$123.27	$123.25	$123.30
Purchase #7	$39.29	6.590%	$41.8792	$41.88	$41.90	$41.90
7 purchase totals =	$793.25		$876.0810	$876.08	$876.05	$876.10