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	$246.99	3.427%	$255.4543	$255.45	$255.45	$255.50
Purchase #2	$64.71	6.347%	$68.8171	$68.82	$68.80	$68.80
Purchase #3	$33.27	6.773%	$35.5234	$35.52	$35.50	$35.50
Purchase #4	$96.51	4.379%	$100.7362	$100.74	$100.75	$100.70
Purchase #5	$164.40	13.334%	$186.3211	$186.32	$186.30	$186.30
Purchase #6	$185.65	6.860%	$198.3856	$198.39	$198.40	$198.40
Purchase #7	$129.32	6.175%	$137.3055	$137.31	$137.30	$137.30
7 purchase totals =	$920.85		$982.5432	$982.55	$982.50	$982.50