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	$19.70	7.281%	$21.1344	$21.13	$21.15	$21.10
Purchase #2	$55.49	12.839%	$62.6144	$62.61	$62.60	$62.60
Purchase #3	$175.75	10.349%	$193.9384	$193.94	$193.95	$193.90
Purchase #4	$90.90	10.149%	$100.1254	$100.13	$100.15	$100.10
Purchase #5	$49.91	11.221%	$55.5104	$55.51	$55.50	$55.50
Purchase #6	$117.91	3.811%	$122.4036	$122.40	$122.40	$122.40
Purchase #7	$46.66	12.558%	$52.5196	$52.52	$52.50	$52.50
7 purchase totals =	$556.32		$608.2462	$608.24	$608.25	$608.10