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	$20.49	10.123%	$22.5642	$22.56	$22.55	$22.60
Purchase #2	$100.54	3.751%	$104.3113	$104.31	$104.30	$104.30
Purchase #3	$40.80	5.193%	$42.9187	$42.92	$42.90	$42.90
Purchase #4	$136.44	13.462%	$154.8076	$154.81	$154.80	$154.80
Purchase #5	$192.72	3.760%	$199.9663	$199.97	$199.95	$200.00
Purchase #6	$157.36	8.841%	$171.2722	$171.27	$171.25	$171.30
Purchase #7	$139.46	3.447%	$144.2672	$144.27	$144.25	$144.30
7 purchase totals =	$787.81		$840.1075	$840.11	$840.00	$840.20