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	$220.57	9.226%	$240.9198	$240.92	$240.90	$240.90
Purchase #2	$100.33	7.338%	$107.6922	$107.69	$107.70	$107.70
Purchase #3	$166.38	3.577%	$172.3314	$172.33	$172.35	$172.30
Purchase #4	$27.99	13.400%	$31.7407	$31.74	$31.75	$31.70
Purchase #5	$224.51	4.147%	$233.8204	$233.82	$233.80	$233.80
Purchase #6	$64.83	11.607%	$72.3548	$72.35	$72.35	$72.40
Purchase #7	$47.79	4.764%	$50.0667	$50.07	$50.05	$50.10
7 purchase totals =	$852.40		$908.9260	$908.92	$908.90	$908.90