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	$27.75	12.252%	$31.1499	$31.15	$31.15	$31.10
Purchase #2	$130.84	6.734%	$139.6508	$139.65	$139.65	$139.70
Purchase #3	$87.65	3.492%	$90.7107	$90.71	$90.70	$90.70
Purchase #4	$80.96	10.497%	$89.4584	$89.46	$89.45	$89.50
Purchase #5	$187.90	11.373%	$209.2699	$209.27	$209.25	$209.30
Purchase #6	$109.38	10.642%	$121.0202	$121.02	$121.00	$121.00
Purchase #7	$238.37	5.663%	$251.8689	$251.87	$251.85	$251.90
7 purchase totals =	$862.85		$933.1288	$933.13	$933.05	$933.20