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	$9.57	13.341%	$10.8467	$10.85	$10.85	$10.80
Purchase #2	$181.66	12.645%	$204.6309	$204.63	$204.65	$204.60
Purchase #3	$59.70	6.686%	$63.6915	$63.69	$63.70	$63.70
Purchase #4	$38.77	11.321%	$43.1592	$43.16	$43.15	$43.20
Purchase #5	$109.66	13.474%	$124.4356	$124.44	$124.45	$124.40
Purchase #6	$174.43	12.685%	$196.5564	$196.56	$196.55	$196.60
Purchase #7	$64.78	11.744%	$72.3878	$72.39	$72.40	$72.40
7 purchase totals =	$638.57		$715.7081	$715.72	$715.75	$715.70